this is kinda turnin into a building fund forum. the building fund isnt just to replace stuff (renovations) in the church but to maintain the church, like pay light, gas, phone, and water bills, property taxes, loans, and rent (for churches that dont own the place they're in), all of which an average member doesn't see, but benefit from nonetheless.
there is a strategy to alleviate the original problem. if equipment care and maintenance were considered and included as legitimate church maintenance expenses (which already probably is for the house system) then your problems of bass care would be taken care of. note, however, that if you want proper care or something done of your choosing, you may have to pay out of pocket at the time and get reimbursed by the church afterwards, which is how my church does for drum equipment. otherwise u'll have someone who dont know a bass from a guitar taking care of that, like buying strings for u or taking ur bass to a shop for maintenance, etc., which u most likely dont want.
the musician fund makes sense in theory, but i have a feeling that people will start paying towards it based on their feelings of your performance, which could go from legitimate to outright stupid. For instance, a choir member could say "none of the musicians showed up for rehearsal this week so im not giving anything" (legitimate). but then u could have a member on sunday morning say "i didnt like the songs they played today so im not giving anything (totally unfair). it could be done as a supplement to what the church put aside, but not as the only source, unless its a church that cant afford anything at all.