Any spells out there (Any MM game) that you think are usually ignored, but can be quite useful when applied in a given situation or in a certain way?

I've got one for MM7: Detect Life.

At basic level at beginning of the game I thought this has got to be the most useless spell ever. 10 mins per skill point, means you have to cast it during or just before combat to be effective. So you waste a turn, a spell point (which at this stage you don't have all that much) and all that so you get the monster's HP. What for?

Now at grandmaster level I once cast it accidentally, and was pleasantly surprised to see how useful it is. With duration one hour per skill point and 10+ skill points, it means that you cast it once at beginning of day and forget about it. For one measly spell point (of which you have tons) you get something, for which you had to obtain a special boss item in MM6!
Unlike ID Monster skill, this gives you current HP. And while maybe it's something you could do without, nevertheless it's a pretty neat addition, considering the low costs of casting.

So far I've only played MM1 and currently working through MM2 (hoping I'm getting towards the end ...) but I've only recently started using Acid spray having ignored it until now. most of my party are around level 22 having completed the specialist quests) so I've had the spell for a while and only started using it during the clerics quest when I had to find something to replace the mages damage spells.

In MM1 Make Room was something that was useful in certain situations (allows the first 5 characters to do hand to hand combat). Did mean a lower level party might be able to take out a creature before it gets to attack.

Dragon Sleep in Might and Magic 5. That spell actually works pretty well.

That spell does not work well in MM4, however, as the dragons there have much higher index numbers.

There's also the spell that paralyzes beasts, and it actually works on those armadillo monsters.

I remember this being the only way to deal with them for players who were starting a new game in MM5. Those who had already finished MM4 were powerful enough to tackle them head on, but lower-level parties needed to rely on the paralyze spell to take them out.

Actually, there is one overlooked spell in Might and Magic 2: Uncurse Item. Nearly all players see this spell but don't see any cursed items, thinking this spell has absolutely no use. Turns out that it actually does have a couple uses.

First, the description of the spell is completely wrong. It does not actually uncurse an item (even if you do manage to get a cursed +63 item). Instead, it sets the number of charges remaining to 1. This has two uses that I have found:

1. Sometimes, an event will give you an item that has a spell, but has no charges. Recharge Item does not work on items with zero charges, but Uncurse Item will. You can then add charges via Recharge Item and cast the spell normally.

2. If you equip an item that boosts a stat when equipped and use up the last charge, causing it to break, you will keep the stat boost permanently. This allows you to permanently boost AC and Resistances. By casting Uncurse Item, you can quickly get the item down to 1 charge remaining. (I forgot whether the item has to be used during battle or out of battle, but I know there is a bug that causes only one of them to work.)

Note that I have only tested the DOS version: there's no guarantee other versions will behave the same way, especially when bugs are involved.

By the way, trying to equip a cursed item will curse the character, and a cursed character, I believe, can't equip anything.