one option that has been overlooked is to upgrade your bass. do you like the way your squier plays? if so, upgrade parts! it's cheaper than buying a new one and you can save your money for a really nice bass in the future (why pay $400 now and then want to buy a $1000 bass in a year or three?).
my first bass was a squier p-bass that i have modified so much, it really isn't a squier anymore. i've changed everything to the point that the only original part is the body itself. new neck, new pickup and electronics, shielded, new knobs and pickguard, new bridge, new tuners, new neck plate... but i was able to do it over time as i had the money. now my bass looks and plays just as good as any $1000-$1500 fender usa bass, and i only spent about $550 total on it.
i first upgraded the pickup to a seymour duncan basslines spb-3 quarter pounder (seymourduncan.com) ...there is a guy on ebay selling them from arkansas, usa for $55 buy it now with free usa shipping and $10 international shipping. the pickup is probably going to make the most bang for your buck as far as improvement goes. bartolini makes great pickups as well as EMG (if you like active... i personally like passive pickups). others feel free to chime in on what pickups you like for your certain styles of music.
upgrading the electronics (better pots and wiring are a good start) as well as buying a roll of copper shielding tape and shielding the body cavities. a p-bass uses a hum-cancelling pickup, so you don't have to worry too much about that, but often times, cheap pickups and electronics make lots of unwanted noise and shielding and grounding the electronics are a good way to eliminate a lot of that.
next, the bridge... most vintage-style bridges get the job done, but don't give a whole lot of sustain... uprgade to a high-mass bridge for more sustain and improved playability. i am partial to leo quann badass II bass bridges (about $60-$70) and they improved the sustain and playability a lot from the squier bridge i had before.
tuners: tuners can make a difference in stayng in tune for longer as well as improving sustain. about $50 for a good set of sealed tuners. a worthy upgrade.
looks: usually squiers come with a single-ply white plastic pickguard and they look really cheap. i have a cream body, and i bought a tortoise shell p-guard for it which improved the overall look a lot. i currently have a black/white/black 3 ply p-guard on mine now and it looks great with the body. pickguards are $20-$50 depending on material. i also changed the knobs from the shiny chrome barrel knobs to black jazz bass knobs (fender knobs cost under $10 for the set.
as you can see there are a whole lot of options with making your bass better. i've built two already (both fender-style with mainly fender parts) and it is a really rewarding experience.
i hope that helps a little!