Having a magic-user or two in the party with some artillery spells kept in reserve for emergencies can often turn the tide of a close battle, or give the party enough wiggle room too to escape when an encounter is really going against them. Spells like sleep, hold person, and fear can mean the difference between a successful fight (or flight) and a dead band of adventurers. However, I've seen the tendency for players (including myself) to memorize offensive spells over defensive or utility type magic, particularly at lower levels when the fire power is needed to deal with the toughest opponents a party might encounter.
In First Edition, magic-users can memorize the same spell more than once. I think its tough to resist the temptation to slot in a couple of sleep or fear spells (crowd control), magic missile or a silence (to disrupt enemy spell casters), or a few fireballs or lightening bolts to soften up opponents before a big fight. This tendency leads to other spells being ignored, which in my opinion has a detrimental effect on other aspects of game play. Utility spells in particular can be the difference between a party finding magical treasure or traps, fully exploring a dungeon and discovering its secrets, and so on, but these are often passed up for offensive magic.
Probably the easiest answer would be to simply have more spell casters in a party. This approach may not work for a small group, however, as I think there is a threshold for how many characters each player can run and keep track of effectively. Further, it'd be great if we could all have four or more actual players at the table at any one time, but for many of us with families, careers, and so on, its simply not possible. Some groups grant low level spell casters more spells; I'm not totally against this, and even Gygax offered access to "cantrips" to give low level magic-users a few more options. However, I think bonus spells for high Intelligence probably goes too far, while "cantrips" are pretty weak and don't go far enough. Perhaps some of the simpler, low-power first level spells could be re-tooled as "cantrips" to offer the low level wizard a bit more diversity in his spell selection. Some candidates that might be re-tooled for use as "cantrips" or 0-level spells might be affect normal fires, detect magic, erase, magic aura, message, or read magic, with the idea that the low level magic-user has mastered these "cantrips" during his apprenticeship; perhaps Allow the use of two or three of these "cantrips" or 0-level spells per day, in addition to the regular number of spells.
That being said, some folks don't like bonus spells for various reason. The magic-user starts very weak, but gains great power over time if he is smart and can survive that long Some thing that bonus spells ruin this essential part of the archetype, or disturb that most sacred of cows, "game balance." The notion of "power creep" often enters such discussions as well; if you give the MU more spells, what does that do to game play, and what do other classes need to be on par with the power of the MU? And if the fighter has to be "bumped up" to keep that class interesting and fun to play in comparison to the new goodies for magic-users, then what do we now need to give the cleric or thief? And if what the Referee and the players really want is greater access to spells and abilities in the first place, then why not simply start characters at 3rd or 4th level, rather than altering the paradigms given in the rules?
My wife is taking a turn as Referee for our family campaign (using Joe Bloch's fun Castle of the Mad Archmage found HERE), and I am running a few characters at the same time, one of them a magic-user. After gaining a few levels and having access to greater number of spells, I made sure to have a few sleep spells memorized at all times as a "get out of jail free" card. I knew that other spells would help us to explore the dungeons, but felt we needed the fire power, especially against groups of humanoids that could gang up on us in the upper levels.
Our family campaign operates with the idea that the rules are subject to reinterpretation, tweaking, and elimination if they are deemed to hinder play or create too much book keeping. We are using First Edition as our base, but want to allow those rules to be tweaked and altered in an organic fashion through play to decide what works for us and what doesn't. So, we've had different discussions about the tendency of players to memorize mostly offensive spells, and I had expressed my view that have two or three sleep spells memorized at the same time seemed kind of lame. Still, it was hard to break away from the "safety net."
Originally I figured that scrolls of spells would mitigate this tendency to memorize only or mostly offensive spells. However, its been our experience that low level characters need those scrolls to add new spells to their spell books.
After pondering this for quite some time, the simple answer struck. We ruled that any particular spell can only be memorized once per day, eliminating the ability altogether to memorize the same spell more than once. This has forced the players of spell casters to choose other spells, and frankly its made a big difference. We have fewer "get out of jail free" cards to play, but that has had a positive effect on our game play as well. We approach encounters with more caution and circumspection that we used to, and the use of other spells has led to better dungeoneering.
Now of course, it could certainly be said that the real problem (if you view an emphasis on offensive magic over and above other spells as a problem) was our style of play and poor gaming habits, and I won't deny that there is truth to that. However, by disallowing the memorization of the same spell multiple times, it has actually broken this habit for us, which has been a good thing. While it places a new restriction on spell casters, it also forces the player to think about the other spells in his repertoire and make use of a wider variety of them.
On the flip side, we allow players to reverse spells the character has memorized as long as they are listed as reversible. This adds a nice bit of diversity and flexibility without resorting to granting "bonus spells."