Should I power up this Pound/Dazzling Gleam Blissey?

have you already checked the cp difference between her and a perfect one at lvl 40?

This are arguable the best moveset. ZH/DG is tech #1 for what people are using against her but roughly their the same. I'd definitely power her! Congrats

if no way to find another one or better one, and have stardust and candy to spare i would just power it up to lvl 30 max, so it has decent cp to leave it in gyms, past lvl 30+ i only power up 90+ ivs with good moveset for defense or attack

IMO, i will wait for a better IV one for putting in a gym or a better moveset as a gym attacker

She has a strong attack stat and top moveset, which are most important. I'd max her out.

Because Blissey's stats are so unbalanced, a lower IV one with a high attack stat will often have the higher CP. Compare her to one with 10 attack and 15/15 S/D and you'll see.

Blissey is primarily a defender. Although she is a good attacker, she doesn't hit hard and the battles get long and boring.

How many CP does she need to stay in your local gyms reasonably safely without being churned out?

Power her up to that point, but no more. More won't do a better job getting your 10 coins a day.

If that point is way high (which it is in some areas), to the point that powering her past L31ish won't get you enough CP, consider not powering her up at all. Get yourself a Dragonite, Gyrados, or Rhydon with greater CP or you'll just get churned out.