Hi Thomas
If you need any kind of justification then get them to take a look at the ease and power of the dynamic query API - blows everything else I've seen out of the water in terms of how intuitive it is. Add to that the level of support you get as a customer here and the ever expanding list of features and there's really no doubt which to chose in my opinion.
While things like an automatic ASPX admin template no doubt add something to the mix, I'd only really see things like that as a skeleton anyway so I wouldn't think of them as part of my buying decision, just a nice little bonus that may or may not get used.
Also, don't forget that you can still use the old templates with MyGeneration which is open source anyway.
Just my 2p
Cheers
Martin