Mike,
We moved up to a 1999 Mariner 350 this year, from a Regal Commodore as well (albeit 25').
We LOVE IT. Absolutely is a great boat for entertaining and cruising. Word of caution though about family cruising - there is only the one stateroom at the front - kids sleep on the sofa turned bed - and/or dinette turned bed (the dinette is a pain to get up and down though, I highly recommend the sofa first - it's a breeze).
The things we like best about our boat is the layout below - nice and open and bright - and all one level.
The walkaround is HUGE - I feel very comfortable walking around up there tending to lines and fenders.
The seat up front is FUN FUN FUN - dogs love it and I enjoy it when I can get one of them to move long enough for me to sit down
The bridge is HUGE too - GREAT for entertaining - one weekend we had 6 adults and 2 kids up there for an afternoon cruise - was quite comfortable.
Things we would change: on our model (I think they changed this 2005 or 2006) there isn't a good "outdoor dining" area. The table on the bridge doesn't have seating around it - but it makes a nice "buffet" table. Dinners are down below on the dinette - which can be interesting if there are waves in the anchorage
we are thinking about adding a washdown pump - there is certainly room for it - where we anchor, lots of clay and weeds come up with the anchor - would be handier than the bucket on a rope I currently use
I think those 2 minor things are the only things we would change - but they certainly aren't the "bad" of the Mariner.
You'll enjoy overnights on the Mariner - the stateroom is very spacious and bright - and private. Again, the only downside if you have kids regularly (we don't, ours is 17 so boating has slipped in terms of priority) cause they'd have to use the sofa.
Mind you - we don't spend any time down below at night anyway - and we've had guests overnight who go to bed earlier - we enjoy our drinks on the bridge, on the front seat, or on our chairs out back - and slip in quietly when we're ready for bed.
Anyway, I'm rambling - can you tell I'm still on the "new boat" high?
Jenny