I just went through the same problem of what to do. I probably have about $10K in len's and digital equipment for my digital Fuji S2 DSLR. Started with the Nikon D100 but ended up with the S2 for various reasons not relevant here. Initialially I bought the DSLR for diving, after I got use to taking land photo's, but as I got into it you look at the potential costs for a camera that is outdated quickly. My Nikon len's will be good for a long time but I can already get a better camera. Hence why would I want to spend $1500-2K for a bare housing then another $1K on dome ports and accessories unless I was either diving daily and/or doing it as a profession. Not to mention having to haul it on airplanes. Now add another $1500 - 2K if I want a decent pair of strobes and arms. Its gets expensive.
Which brought me to the C5050 Olympus. Lot's of support. $400 online price (harder to get now though so probably have to get the C5060) so if it floods I don't loose much money versus a $2500 digital (now cheaper but was cost new).
Still a complete setup adds up. The PT-015 housing, Inon D-180 strobe, leak detector, lens store, wide angle, tray, arm = $1500. Toss in the camera and a 1G Sandisk CF card, good rechargeables (> 200 pics) and you are about $2200 complete. On top of that I have found that having only one strobe you are alot more apt to get shadows thus I'll probably spring for another strobe, arm and fiber cable next year adding another $700. Expensive hobby but this is still alot less than a full digital SLR and if I want to get a new camera and housing I'm talking about $1K, 1/3 the cost of and expensive housing with domes.
Live-aboard wanted $600/week rental so I figure my $2200 investment only cost me $1600 and will drop on each additional trip.
With regards to pixels... Fuji is 6.1 Mpix, Olympus 5 Mpix. Fuji takes much better pictures but has nothing to do with the pixels. A lens can cost as much as the camera and my $1800 lens with vibration reduction can work magic (20" X 30" enlargements), $300 lens and you can get alot of distortions (luck of the draw when buying it). Recent underwater trip photo's (C-5050) have come back, many blown up to 11 X 14 and they are awesome. Not what the Fuji would do nor probably the less expensive Canon Rebel with a high quality lens, but more than adequate. You can't put a cheap lens on a DSLR and expect good photo's unless you are real lucky with the lens that is shipped to you.
www.pbase.com/bridgenet/australia
These are reduced to 80K files versus the 2-3Meg used for enlargement but gives an idea of what a first time C5050 user can do, no previous experience except a couple days of C4040 rentals 2 years prior.