I'll answer with a golf story.  A few decades ago, I decided I wanted to play golf.  Not knowing if it'd be any good at it, or even enjoy it for that matter, i bought a set of starter clubs which consisted of a 3 iron, 5 iron, 7 iron, 9 iron, a driver and a putter all in an inexpensive nylon bag.  i played with those clubs for a year or two and started to develop enough skill that I was only embarrassed when I played with good golfers, rather than utterly humiliated like I was when I started.

One day I got assigned to play with a guy that I had never met. I told him that he should probably go on ahead of me since I was a terrible golfer. He said, "Don't worry, I'm not very good either."I was playing my usual bogie, bogie, double bogie, search for the ball in the woods game.  While he played birdie,  birdie, par, birdie, eagle!  At that point I said, "I thought you said you weren't a very good golfer."  He replied nonchalantly, "Well for a pro, I'm not very good.  The Louisiana Open tournament is going to be held here next week and I'll be playing in it." Naturally, I started asking him questions that I thought might improve my game.   So... here's the part that answers your question:

I asked him, "When do you think I should get a full set of clubs? Would that improve my game?"  He replied, "You should get a full set of clubs when you walk up to your ball, decide what club you need for the distance of the next shot and notice that club isn't in your bag. That's when you'll know you need more clubs.  Right now, hitting the ball straight is what you should going for."

Same thing with violin bows, you'll know you need a different one when you know what kind of bow you need and why you need it.  For a long while, learning to bow properly will get you a lot more milage than a different bow.  Assuming, of course that the one you have isn't total garbage. If it is, then I would recommend starting with the fiddlerman carbon fiber bow, inexpensive and decent. and will last you a long time.