Yes and no.
Gear IS important, and if you've got your AM leveled up, then the gear might be what you need to get you over a hump. If you want to buy gear that's blue or green, and rock it to level up an AM that's not a bad idea either.
No because the money you'll have early on is pathetic as fukk
Ive been bullshytting hard in the middle game (chapter 10 right) and the amount of money you pull through regular frontiernav intervals gets ridiculous. There's nothing in the store you'll really need to break the bank over - at the same time, it won't really hurt you either.
Once you get skells though... that'll change. Frames, armor, weapons, replacements are all hefty prices to say the least. That's where most of your money is gonna go.
Said it before, but I'll say it again - DO SIDEQUESTS. Normal missions can unlock some crazy shyt - from the character editor to new AMs to branching storylines and adjacent affinity quests.