should I power up my 96% Ampharos??

Not really, unless you're sitting on a ton of dust. At the end of the day though, if you really like Ampharos and powering it up would improve your enjoyment of the game, go for it.

It isn't for me. I have a 100% one and it's not getting any love.

Raikou & Zapdos > jolteon & ampharos

If you really like ampharos as a mon in general and really feel you wanna power it up do it. Your jolteon I would leave as is or power it up to 30 unless you want acouple different electric attackers but really your best bet is to just power that zapdos and get a good iv raikou and power that up there way better in those roles and much more worth the dust nowadays.

If you are wanting it as an interesting defender, I would--for now at least--keep it under 2000cp so it doesn't get hit by the increased rate of motivation loss that happens at 2000 and higher CP.

Checking the CP calculator, that is taking it up to level 26 with 1992cp, using 39K stardust.

I was getting bored of the game and wanted something fun to play with. According to my 7 year old son he can mega evolve which is kind of cool. Mine has an 82% IV and I powered him up to level 35.5 (I am level 35). Only weakness is Ground and I use him to battle gyms. So much fun. I FTMed and CTMed him and now have Charge Beam and Zap Cannon. He does mega damage and is really easy to dodge with. Made the game fun for me again. Samething with my Ferilgator. Having something rare that brings fun to the game is priceless. I use him in raids as well and people love him. He is tankier than Jolteon and hits really hard with Zap Cannon. I can usually get 4 - 5 zap cannons off in a raid! I have a ton of good generalists but he is my go to favorite. Take it for what its worth! Have fun with yours!