Hi @TheLazyDuchess, there's no right or wrong way to play the game. Amongst my rl PoGo friends I am derided for hoarding stardust (over 5Mn) but I have 3 maxed out T'tars, 2 maxed out 100% Feraligatrs, a maxed out Rayquaza, a maxed out 100% Raichu, 2 maxed out 98% Garys, a maxed out 86% Red Gary and a maxed out 93% shiny Kyogre.
We all have our favourite 'Mon, mine is Alolan Ninetails. Just because it's beautiful. My best one won't get powered up, she's not strong enough to justify it. But she is gorgeous. :o
So power up your Arcanine, it makes sense to you to do so. Enjoy the game your way, just like most of us do, and you can't really go wrong.
In other news, I get to raid Deoxys next Thursday! Hurrah!