Obviously, resist comes in handy against casters, but not as handy as you might think, provided you have enough mana and/or are willing to use gold to counteract any truly troublesome curses.
Since you're going swords, I will assume that your standard weapons are a Double Axe for WW/DS and Bladed Staff for AI. These are speed 3.25 and 3, respectively. Generally you'll use the Axe against lower stuff, and the Staff against bosses (until you get l3 swords mastery, then you should almost always use the Axe... but again, that's a more advanced question).
As SSI on the suit/buffs is pretty easy to come by these days, I will assume that you can pretty easily get to the point where, when not under any spell effects, you have enough stam to swing both weapons at 1.25.
One way resist can come in handy is against your standard magery debuffs. I believe the debuff equation is 8 + (eval/10) - (resist/10). The strongest casters in the game that I know of have 200 eval, so that's -28 debuff with 0 resist, or -16 with 120 resist. The thing is, even the -28 is totally over come by a Greater Str/Agility pot with 50% EP. Most things, even boss level things top out at 100-120 Eval... meaning as long as you're willing to carry and quaff pots as needed, you needn't worry about this aspect, with the one exception being if you really need the mana from having that extra int.
Resist can lower/prevent being poisoned by the spell, but since you're a vampire this doesn't matter anyway.
Mana Drain can be a problem, and the amount drained is affected by resist, but even still you're going to get it all back in 4 seconds anyway, and against a boss level caster (120 eval) even with 120 resist, you're still going to lose 40 mana, which is likely enough to prevent your next AI anyway. Here too, I don't truly see resist as worth it.
Paralyze duration is reduced by resist - but is rendered moot by simply carrying a trapped box.
Against Mystic casters, of which there are quite few... resist can prevent you from being purged, but even against a really good mystic caster, I'm not sure 100 resist would make a difference, I think you still get purged more or less every time they cast it. Sleep is broken by damage, so again, trapped box. Spell Plague might be useful to have resist, but that depends on how resist really comes into play here. If what is stated on UO Guide is correct, I don't see resist as worth while here...
Necromancy is, IMO, the best use of resist and can really save your life. It will reduce the damage dealt by pain spike (18 vs 30 direct damage when your resist=their SS), reduces Corpse Skin and mind rot duration. Both of which are kinda, 'meh' to me. The real key, though, is blood oath. When blood oath, you do 25% (could be wrong, but this seems pretty close from what I've seen, maybe 20% or 30%, I try not to actually do any damage while blood oathed...) more damage, but take the same back in return. So if you land an AI that would normally do 150 damage, you're going to kill yourself 100% of the time without resist. Per UO Guide "Resisting Spells now reduces a percentage of Blood Oath damage by the following formula: ((Resisting Spells Skill x 10) / 20) + 10 = percentage of damage resisted." So 100 resist looks like it reduces 60% damage, making this a generally survivable event - but you're still going to be out half or so of your HP - so you're still going to be in tough shape.
The thing is, all of these are countered one way or another... generally speaking, you could cast remove curse with chiv, though with only 60, this might not be terribly effective, or you can eat an enchanted apple. Blood oath is trickiest, but you can simply keep an eye out (or mod the EC... I think this is legal) and disarm, so you can run off and get it cleared up - with either remove curse or an apple.
Given the ease of counteracting nearly every negative scenario, I am simply not sure that resist is really worth it in any PVM scenario.
