I can't say much about the Java development environment. But I have done some sites with ASP. I can say that aolserver + OpenACS is a lot better for medium to large sites. ASP is just good for tiny sites or MS shop clients. Also among all web dev enviro I have experienced: mod_perl, aolserver and IIS. I find aolserver to be both superior and easiest to use in DB back end sites. Especially the db API of OpenACS. I can't say much for plain aolserver since I started straight away to OpenACS/ACS.
So if OpenACS will make your live easier, my personal experience is that yes it did make my life easier. Also once you get a hang of OpenACS-4 higher learning curve but more productive in the long run.
I am interested to look at Java environment though. Although not as replacement but as a complementary platform to OpenACS. I think Tcl and Java should be good partners. ns_javablend should be nice, hint hint hint. I hope DanW finds more time again =)