I played with just the HeroQuest minis and some occasional lego figures for years. I have a bigger collection now, but I have no problem with goblin minis representing kobolds. As for PCs, I just have maybe thirty assorted heroes, and people just pick the one they think comes closest, usually based on weapons and armour. One of my players sometimes picks a mini he has, and then makes a PC based on it, so it will fit neatly. I don't much care.
I might have invested in an expensive custom mini for a recurring PC type, but so far it just seems smarter to wait until 3D printing evolves a little further, and I can something done with a friend who is into that sort of thing.