The enhancement value will scale down to what the IO's would grant at that lvl (i.e. a level 50 IO would grant that of an lvl 15 IO when exemp'd to 15th) It doesn't matter what level that enhancement is to begin with.
What does matter when exemping is what set bonuses you can use at that lvl. A full set of lvl 50's will only grants set bonuses as low as lvl 47 (the lowest level one could slot a lvl 50). A set of lvl 30's grants as low as level 27.
A mix is complicated. Let's say you have a full set of Crushing Impact. 2 of them are lvl 30, 2 are 40 and 2 50:
At level 47 up you gain all 5 set bonuses.
At level 37 and up only 3 of them would 'count' toward the set b onuses, and you'd lose the 2.5% Psi resist and +5% recharge.
At level 27 and up only 1 would 'count' and you would only get the 2.2% immobilize reduction.
I personally try to slot lvl 37 IO's so I kept set bonuses at lvl 34+ (good for the higher level arcs and I hit the ED cap fairly well) 
The plastic tips at the end of shoelaces are called aglets. Their true purpose is sinister.
--The Question, JLU
Or you could use the dual build option and have both, at twice the price :/
The more people I meet, the more I'm beginning to root for the zombies.
Do SOs scale?
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Do SOs scale?
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No. I'm also reasonably sure that set IOs don't either. The only loss whenever you exemplar down as far as I know is the loss of powers that you are now too low level to use and set bonuses that use set IOs that are higher level that you would able to access at your exemplared level (exemplared level + 3). Even procs still function at full effectiveness for your level as long as you've still got the power with the proc in it.
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Do SOs scale?
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No. I'm also reasonably sure that set IOs don't either. The only loss whenever you exemplar down as far as I know is the loss of powers that you are now too low level to use and set bonuses that use set IOs that are higher level that you would able to access at your exemplared level (exemplared level + 3). Even procs still function at full effectiveness for your level as long as you've still got the power with the proc in it.
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If you have enough enhancement strength in a power (from actual enhancers), it will get reduced regardless of whether its from IOs, HOs, SOs, DOs, or a mix. For the actual mechanics of how enhancement value is calculated, I refer you to the ParagonWiki Article.
[edit: Iirc, going into the enhancement screen while exemplared should show you the degraded enhancement values.]
Thanks for all the information and the link is exactly what I was looking for 
I am a returning newbie, my goal is to maximize my BS/WP powers/slotting so that I am able to make the most use out of my enhancements as I go along even after I am higher level and doing the flashbacks, should I maximize the slots in the lower level powers so that I get the most out of them when i am exemplared. Basically should I bias my slotting to the lower level powers and put the best set/uniques in them to maximimze their benefits for the long haul? Also should I use lower level sets to ensure they still perform at the lower end, I am still not sure if a level 50 enhancement in a level 16 power does any good below level 47.