Do it. F2P is generous enough. Some things take longer, but you eventually get a good character or two purely from weight of numbers drawn. I had a dry spell from soft launch but then pulled Noctis. Nothing else of note but the decent 3* and 4*s eventually come to you and you don't NEED a party of base 5*s. TMs make any team relevant for a start and just because you're F2P doesn't mean you won't get lucky. Pretty sure I'm better off unit wise than some who do paid 11 pulls every now and again.
Paying means you've a higher chance of getting something you're chasing. But not spending money means you've a higher chance of not going insane/depressed/broke because of a mobile game. A bedile with earned free lapis just gets a shrug and you move on. A noctis with free lapis is actually an extra awesome feeling with no money spent guilt or shame attached. I'd some party in my head that day. You don't get that if you spend money. It also kind of feels like paying for cheatcodes or something. Much more satisfying to take down Greg with your hard earned and worked on units than spending a small fortune and beating him in one turn with a pack of Noctis' (Nocti?) Where's the fun in that?
If I'd an insane amount of desposable income I'd probably do a paid pull or two every now and then, but don't have such luxury and if I came into such money now I think my mentality to not spending money on gatcha games has become so ingrained I'd probably still talk myself out of it.