If the boss has a specific objection, go after the objection. For example, if he says that the update might introduce bugs, use a bit of personal time to make a private build that compiles right under Delphi 2009. (Unicode issues notwithstanding, this shouldn't be too difficult or time-consuming unless you're using a ton of third-party libraries that can't be updated easily.) If you can, get a supportive QA engineer to help out by running tests against it so you're sure it's pretty solid. Once you have a good build, then run a demo for the boss.
Once you've shown that basic functionality works more or less as expected, then show the boss all the productivity-enhancing features of the new version, like SyncEdit, built-in refactoring, new syntax that wasn't available way back in D7, new debugger features that help track down and remove any bugs that do get introduced faster, etc.
Show the boss that 1, you've already got the port created and ready to check in to source control with his approval, and 2, this provides benefits both to the developers and also the clients, he's a lot more likely to see the upside. One of the biggest benefits he can turn around and show to other people is Unicode support, especially if you're trying to sell to any international customers who use a non-Roman alphabet.
(Yeah, this was pretty specific to Delphi, because I know Delphi real well. But you can apply the same principles to just about anything. Also, if at all possible, try to update to Delphi XE. One of the biggest new features for developers is Generics, and they were pretty badly broken in D2009, and mostly (but not completely) stable in D2010.)