I guess whether it's worth it is up to the individual. If you don't have the money to spend then the answer is probably no.
There is more than a horsepower gain when buying aftermarket heads. They usually come with modern valve componenets (stainless undercut valves, springs, keepers, valve guides, pushrod guides), and they are setup for stud mounted rockers. There is also the weight advantage with aluminum heads.
You originaly stated that you wanted to make good power and retain a smooth idle. Since that rules out a lumpy cam I believe that the next logical option is aftermarket heads. I don't think it makes sense to put heads that flowed poorly on a 289 or 302 on a 331 stroker.
[ February 24, 2003: Message edited by: David Sanchez ]
[ February 24, 2003: Message edited by: David Sanchez ]