Cheap tweaks...What would YOU reccomend?

Cheaper than cheap: Turn off the lights. I don't know why this works (probably by removing distractions?), but I frequently find I enjoy the sound more with the lights out.

I also find that cleaning my ears with one of the ear wax removing drops from CVS usually helps when my system doesn't sound as involving as usual. I recommend trying this if you've never done it before, especially if you wear earplugs occasionally.

A degaussing c d disc.This will dramatically improve stereo separation,and clarity.And not expensive. Atlas and Isotech.

Just tried this and it worked like a charm...

I've been wrestling with speaker placement of my rear ported speaker
- toe-in the speaker and the bass is detailed, but the image sucks
- the closer to no toe-in and the bass becomes boomy and muddy, but the image is great.

Room size and WAF is the limiting factor! (no big damping screens allowed)

Enter the PERKO boat cowl vent...

Just attached this over the rear facing vent to direct energy downwards and VOILA - can toe-in for the best image and the bass is consistent

http://www.nauticexpo.com/prod/perko/boat-cowl-vent-21871-50697.html

Cost $55 - and they look nice - other makes/sizes are available from your local marine store

Guess you could try firing it at any angle. but down seemed to work great

Have tried damping the speakers rear port with foam, but the sound was not great - this solution allows the speaker to perform as designed

Not really cheap - but less expensive than replacing the speaker

Upgrade your fuses!
This may have been mentioned before in this copious thread. I cannot emphasize and recommend the difference this simple, relatively inexpensive tweak can make highly enough!
If your system is HARSH this will make it smooth, if you desire more definition this will improve it. If you desire greater clarity, cohesiveness and bass control these can help.
I have upgraded the fuses in every piece of equipment own an have yet to hear a definite improvement.