Of course Sense and Android will run more smoothly on a 1GZ processor. The other big thing I like from the spec is that the Nexus One has a wifi chip that supports the N wireless standard as that is a tremendous increase in speed over the G wireless standard.
Beyond the two items above, the other specs are kind of meh... The bigger screen is nice, but it adds heft. I don't play games or watch movies on the phone so the amazing AMOLED screen is not something I would choose to pay for (it may be a big plus for someone using their phone heavily as a multimedia device)
I think that the Eris processor, though older, is capable of running Sense and Android fairly effectively. My guess is that all lag is eliminated by the Snapdragon processor so it's simply a matter of what your tolerance level is. The biggest key for the Eris is that it runs well after the Android 2.0/2.1 update. A lot of posts dealing with the many issues that the Eris has all hang their hats on the fact that after the update all problems will be resolved. While that's an unrealistic expectation, I am expecting that the Eris will be more stable and more responsive running the latest version of Android. If it's not, I'll have to move on to an Android device without Sense.
I'm not sure about anyone else, but the biggest thing I want out of the Eris is simply for the current feature set to work well. That means no lockups requiring a battery pull, no issues running YouTube and reasonable performance (i.e. some lag is ok)
I've had the Moto Droid and the 2.0 functionality does a lot of what Sense does (just not as elegantly). At Android 1.5, Sense is a huge benefit but that's not the case with 2.0. Given that most of the problems people are having with the Eris occurred after the last Sense update, I think that HTC needs to get this 2.0 update right or people will start to abandon Sense as the cons of a device with Sense will outweigh the Pros.
The bottom line answer to the OP is that I am not jealous of the Nexus One as long as the 2.0 update for the Eris results in a phone that is stable and can run Android & Sense efficiently.