Well I guess it depend on the toon you were thinking of trying to add it to.
If you can only add a small amount then I would say its not really worth it and you be better off slotting for something else such as recharge.
Heros
Max Powerz: Lv 50 Tanker
Villains
Max Khaos: Lv 50
Overlord of E.V.I.L.
My Brute - http://maxy-khaos.mybrute.com/
LF SG! Arc ID# 193083
I can get about 20-25% ranged(avoids the dr cap at 30ish) and get some resistance(40% iirc) to weave on top of bodyguard mode(thinking soul for soul storm for -fly and the damage).
Or i could get the obvious mace for the -jump iand -fly in the immob and hold plus the shield that i can stack up to 30 to all types but without any resistance besides toxic.
Problem is most people have probably slotted for acc and tohit to such a degree that most of my defense would probably be negated.
Should i bother with defense?
I have concentrated on defense and regeneration myself, on my Inv/SS tank. The defense is at roughly 30%. It makes a significant difference for me, though it depends on the opposition. Invulnerability benefits from significant def debuff resistance, which means debuffers are not as large a problem they could otherwise be.
The enemies I have trouble with are Superstrength Tankers or Brutes. In addition, I have found it pays to back off whenever Aim or Buildup goes off as it will negate my defense.
If you want numbers, for me 30% defense to S/L is sufficient to reduce most Superstrength opponents (not all) down to roughly 85% net ToHit, from 95%.
Other opponents are usually reduced down to 60% net ToHit.
Is it worth slotting for defense if you don't benefit from elusivity?