There's a lot of misinformation here, so I'll try to clear a few things up.
for arcane, I believe all stats are pretty close in value
While the stat weights for arcane are perhaps less skewed than some other specs in the game, that doesn't mean that the different stat weights don't matter. If you take a look at
the sticky in the Arcane forum, you can see that the generic stat weights show that Vers is 20% more valuable than Crit for example (you would, of course, want to get your own personal stat weights for your character).
so I usually chose the higher iLvL piece of gear no matter what
You should
never blindly equip a piece of gear just because it has a higher ilvl. Instead, you should always sim yourself to see what gives you more DPS (unless it is an obvious upgrade, such as a higher ilvl version of the same item or an item with your best stats). You can check out
this post about how to sim yourself and get stat weights for your character. The short version is that you should get the simc in-game addon that will allow you to export your current gear to Raidbots.com in order to do the simulations. Remember that you'll want to get new stat weights every so often, as they'll change slightly every time you equip a new piece of gear.
I usually equip the stuff that gives me the highest iLvL so that it shows up in the search tool of the raid leader to get me into groups easier
This is not how the group finder works. When you use the group finder tool to apply to PUGs, the number that shows up is your "bags" ilvl. This means that it looks at what your ilvl would be based on all of the highest ilvl items in your bags and in your
bank as well. Therefore, you should feel free to just stash those unusable high ilvl items with bad stats in your bank for the purposes of inflating your ilvl when applying to groups, since it literally doesn't change anything to have them equipped. You used to be able to see this number on the in-game character sheet, but Blizzard removed it by default from this location and from the Armory as well. If you want to be able to see this number again in-game, I would recommend the addon DejaCharacterStats, which brings this number and a bunch of other stats back to the character screen.
PVP
On a completely separate note, things work much differently in instanced PVP, just in case that is something that interests you. In instanced PVP, the only thing that matters is your ilvl. The game assigns a pre-determined template of stats to your character based on your spec, and this scales with ilvl. All set bonuses, trinkets, and legendary powers are disabled. So, if you do arenas or BGs, for that content
only, you'll want to equip your highest ilvl gear and pay no attention to the stats, since you'll be given different ones anyway.
As a pretty casual, non-mythic raider, so far I was far more concerned with doing my rotations correctly, integrating them well with fight mechanings and timings and, as a caster, minimizing my movement. But simming is definitly something I'll look into next.