You don't ask yourself that, you ask the player.
I've never met a player who wants to play a gimped PC fro a whole campaign but getting in a dire spot for a single encounter is quite fun to most mature players. I wouldn't try that while teaching D&D to a 14 yeard old nephew, obviously, but most adult wouldn't mind IMO.
Fights are not exciting without a serious and credible possibility of character death. There are many way to achieve this level of tension and having a few handicapped party members for a fight is one way to do it. As long as it's not an every session occurence, that's quite fun.
If you want just something occasional then you don't need this rule as it can pop more than just "occasionally". Namely, any time you're sleeping anywhere where there's a chance of a random interruption. The DM doesn't always have to tell the PC's when he'll be checking for that either...
If you wanted something to just make it a
little more challenging, then pick something that weakens all players equally, not just those of specific builds. For example, you could have a powerful Wizard enemy that used an ancient and forgotten ritual that strips the PC's armor of all enhancements temporarily. Everyone would still have armor on of course, but they would lose the properties/powers and those extra "pluses" of magical enhancement.
If everyone was level 16 or so, for example, this would mean a drop in AC of about 3 or 4 points depending on how much you've kept your armor up. But it would be
everyone's AC dropping, not just the non-DEX classes. It still means you're getting hit 15-20% more as well, which makes the encounter a lot more dangerous...but it's not insurmountable.
That being said, as long as you built a level +0 encounter, the heavy armor guys won't be in that much trouble if they had Healing surges left before going to camp.
Level +0 encounter are cake walk in normal circumstances so they'll just be a bit harder with the armor guys at low AC.
Level +2 or 3 on the other hand needs everyone in tip top shape and you're headed for a TPK if you do that while the fighter is in PJs. As always, common sense is optional for the PCs but mandatory for the DM.
The enemies I listed were Level +0 enemies, and they were auto-hitting every round. How is that a cake walk? Plus, I picked some basic enemies...if you were looking at enemies that had more attacks that dropped status effects they would quickly cripple your non-DEX PC's in the party because they literally
can't miss except on a 1.