From the AARs I've read, a medium-high level multiplayer game can have each turn can take over an hour. The first thirty or so will be a few minutes - it'll take you a while to have enough troops, commanders and spells to need to finesse anything. Things get considerably longer if you're facing a crucial battle and need to look up your opponent's strengths, test your setups and perfect your scripts.
Dominions is a game I love to read about, but can never justify buying for myself. It's a 55 dollar boardgame that you need 6 to 8 copies of to make fun, and you can't guarentee anyone you know will like it. If it was a fiver I'd probably be handing out copies to everyone I knew.
Think I will just leave this one be for the time being. As you say if it were inexpensive I would go for it, but I have enough games ongoing that I can't really justify the price-tag on something I will only rarely play.