I've played on higher priced basses but I have to say my Matt Freeman sig P, sounds as good as many of them. Really it comes down to knowing your budget. Get the best instrument and amp you can afford and work your ass off.
Im looking to switch to flats too. I play the stock rounds on my MII Sqiuer Jazz bass. I want a mellower sound with a bit more growl. My band plays heavy but melodic. I finger mostly but pull and slap some. I was wondering how much difference there is between 105s and 110s on the E.
I think it all comes down to what feels good. Buying gear is like anything else. Your proud of yours, someone else comes along wit something fancier and you think... damnit.
That being said I love my MII squier
Before I bought My Jazz Bass I played a P and Jaguar. I liked the P, but I like the options with two pickups. I play heavy melodic rock, and mine sounds good. In the end, it's all about what "feels right" as lame as that sounds.