Great gear is very important-a good sound makes you play better in addition to sound better. But, it really pales in comparision to musical and performance skills. Everyone knows a great player will still sound great with a crap instrument and a crap amp. As for the op, I don't know anything about subs. I've never been in a band that owned them. I've played through them because the better venues have their own sound.
When I was a kid, I wanted a marshall stack. I asked a more experienced player what he thought. He said save your money, when you NEED a marshall stack it will be there. He was right. When I really needed one, it was provided by the promoter.
I know some kinds of bands need to provide their own PA, but even though I've played a few thousand gigs, no band I've played with since the 80's had even a mid level one. I can't even imagine how much I'd want to charge to buy, set up, maintain, operate, and haul around big PA in addition to playing a gig. My "big" system is a crown power amp, a reverb unit, a 1604, and some speakers on sticks. I rarely bring it to a gig, usually going with a beringer combo acoustic amp(which I admit is the cheapest acoustic amp I've ever owned) One half of one gig paid for the amp.
Never has this lack of gear cost me money in terms of fees charged or gigs lost IMO. Never has a client asked me about the quality of my gear. I ask the agent what the requirements of the gig are, and if they exceed my gear, I tell them to rent.
I know full time players who obsess about gear, and buy the latest greatest stuff. I don't see how they net any money, in fact I know they don't. I know other guys who are full timers who endorse instrument companies-these guys get all the stuff for free. I don't think investing in band gear, as opposed to personal gear, is a good idea. Even personal gear-I've waited until there was a need that justified the purchase. Again, when a band is ready to do work that absolutely requires certain gear, it has a way of appearing. At least IME.
What makes a band more valuable? Anything that improves it in any way.