Just for my two cents, I've been living aboard a Columbia 34 for about 2 months now.
The high clearance for headroom inside the boat is quite nice. Especially since I am 6'2". There is a clear lack of storage on this boat, and I am just one person living aboard. I have occupied the quarter birth with boxes for storage, as well as every locker. For two to liveaboard, I would recomend modifying the settee for additional storage. Remove the back cushions, cut out the fiberglass behind them, then create some doors out of that glass, and use the empty space there for additional storage. I will be doing this project, and it was recommended by another person using a 34 as a liveaboard.
Also, I don't know if youve got canvas over your cockpit or not, but IMO its a necessity. Having that additional area to occupy that is protected from sun/wind/rain, is very nice.
Another downside I found, is that the storage for the wastewater from the head is quite small. I try to avoid using it as much as I can. You could probably increase the tank size under the V-berth.
I know lighting was an issue for some on the original electrical system for cabin lights. They seemed scant. Luckily, my boat was redone and now has a ton of cabin lights. I would recommend adding some.
Also, a really annoying thing I found is that the plugin for shore power is on the transom, so if you end up docking with the nose in, you have to have a very long shore power cable. If it's not long enough, you either dont reach, our you also have to run the cable down through the cockpit area, and then the cable runs over lazerettes and is just awkward for accessing the cockpit area in general.
I set my boat up with a mini-fridge on the port side behind the icebox, and a microwave on the sliding chart table. Though this ends up being a pain when sailing and need access to charts. There doesnt really seem to be an adequate place to put the microwave.
Also, the freeboard is cumbersome for some people on the boat. I happen to like it and dont find it an issue, but some "larger" people that have sailed with me find it a small problem. Ive found it's easiest to shove off from the dock while onboard using a boat hook, than walking next to the boat on the dock and jumping on.
Also, be sure to check your lifeline stanchions (sp?). I had one that leaked. From other 34 owners Ive talked to, it was kind of common. Was really easy to fix.
As far as the upsides go, Ive never slept better, it's a high and dry sail, and seems quite forgiving. The deck is very roomy, and overall it's been a great boat to live on.