I only Ski occassionally, but the bro's a pretty skier/wake boarder and my Pa used to be right into it. As you say, something that the whole family can get into. See quite a few V8 boats around, but I've only seen a couple that will turn up every time and run properly and that's probably down to the older motor's requiring a bit more attention than what their owners are giving them. I really can't see why you'd have that much trouble with them as long as you start with a resonable unit. All the V8's go well once they're running, no doubt about that.
My Brother bought his boat to be multipurpose though and originally bought a boat for diving, just that the skiing has become easier to do than finding a diving partener. He's got a 90hp Merc (budget a $100/hp for new) on the back of a 16-17ft Fibreglass boat which has a pretty big beam and really I don't think you'd want much less than that. We've skiied for most of the day and managed to chew up 2 (20lt) tanks, but that's wakeboarding and single skiing. The 90's fine for Wakeboarding, though some fat sacs in the back to kick up the wake would be great, but require more grunt of course, we've had sand bags and it was OK, but not fantastic, that's where a dedicated boat would be better. For the single skiier it works fairly well pulling you up and by the time you're up to speed it's pulling a few revs, but then my Bro's not a huge guy. If you're 6ft and 110kgs, you might slow it down a bit.
I've been told not to bother with jet boats. You need a prop in the water for hard turns otherwise the skiier will pull the boat around. Mind you, I saw a jet ski out last time that didn't seem to be doing too bad, but then they're not cheaper either.
I think a V8 inboard would be a nice thing, but like other have suggested, you'd need to be pretty serious about it before you went and propped the money for a boat that could be only used for skiing.
If you're close to a nice skii lake (1/2hr or so) you'll find the time to get out there. We've found that generally when we want to go skiing as a family it's on the long weekend's and every man and his dog are at the same lake and you'll always find a couple of guys that need to be talked to as they're not following the direction rules, but even if they're all behaving nicely, unless it's a huge lake, you'll get cross chop and that gets old quickly, works you pretty hard.
My brother doesn't get out with his boat much now (un-reliable skiing parteners, almost as bad as trying to find diving buddies) and since they've closed down the local skii beach, it has ruined it a bit for him, otherwise he was getting home from work and going skiing every night, but you need someone who's on the same schedule as you. So you can get pretty good use out of the boat, but as others have mentioend, it's mostly for the summer only.
The equipment costs are up there, but not as bad as some hobbies can be, and unless you're chasing the latest and greatest they'll last a long time. We've got some old wooden ski's for the noobs, and old finned board for the noob wakeboarders (me) while my brother has a muh sharper unit and then we've got some quite old, but still in real good condition single ski's. PFD's are a must, and a little pricey, but again last well if looked after. Ski ropes are really the only expendable and hardly a bank buster.
A bit of planning and thought up front and you can get a lot of enjoyment for a modest input and young or old I think the kids will get a lot of enjoyment out of it, you'll probably end up with a lot of hangers on in the years to come.
Bit of a long winded post, but tried to answer all your questions.
