Should I? Would you?

I'd say go for it. You can't predict the moveset anyway so the longer you wait the longer you might be disappointed... Squirtle is the least rare of the starters, so you will be able to evolve another one sooner than you think. Evolving new ones is fun, enjoy it!

Evolving pokemons is a fun part of the game. As you mentioned, Blastoise is not really useful - there are much better water attackers (Vaporeon, even Golduck and Strarmie) and it's a mediocre defender given the low-ish CP and other defender options (Vaporeon, Poliwrath, Slowbro).

I have four Blastoise with different combinations of Bite / Water Gun and Flash Cannon / Hydro Pump and I literally never use them for anything.

"Starters are among my favorite Pokémon(obviously) I've been dying to evolve one"
'"The first I saved up enough candy for is Blastoise."
"80% is usually my cut-off."

i dont see the problem :)

Depends on if you're gonna use it. If so, save up some candy first so you can upgrade it too. Maybe you will get lucky in the process.

Also, blastoise is much cooler than vaporeon, I'd take the hit on stats for the cool factor. Vapes are a dime a dozen.

I evolved mine and I power him up every time I catch another Squirtle. I probably won't use him often, but he'll do an okay job once I get his cp up a bit and be more interesting than another vape. There's not a defender that doesn't have some kind of weakness, particularly now Snorlax has a solid counter.