08 spec b audio limits/options

my apologies if i am retreading settled business, but I did spend an hour going through old threads, searches, and crutchfield first.

I find the 08 spec b audio (no subwoofer, some improvement w/ srs on, have installed a bluetooth for the phone that splices into audio system- the cigarette lighter one) to be a bit disappointing as far as full sound goes. Its loud but tinny for my taste.

Want to improve the overall sound for daily enjoyment, no need to literally shake the earth. Loudness itself is not an issue.

So the questions are:

1. is there line out to splice in aftermarket amp? Does the added power get significantly better performance from the stock speakers?

2. is there an option to replace head unit (or is amplification split from control?) without creating chaos in the electronics (i.e. leaving it looking stock and continuing to function w/ steering wheel controls)

3. most replacement speakers seem to require drilling despite using the same size; have new squeaks and rattles resulted over time?

4. is this hopeless without spending 1500$ after parts, labor and rewiring?

thx in advance for your input.