Having both... having used both, quite extensively as a power user, there is no question... no ifs, no ands, no buts... the TP2 is a superior device. You can argue many points that the TP2 is just not that much of an upgrade and on paper you may be right. From an experience perspective, however, the TP2 is just all around better. Screen resolution, screen sensitivity, speed, battery life, and even hardware ports (3.5mm headphone jack...) this device is just more useable for every day.
Areas I have seen a difference:
Web browsing - there is no comparison - the screen on the TP2 enabled me to check sites with relative ease.
Nav - the larger screen makes it easy to use a it as a navigation device. I have the updated drivers and I use Garmin XT - it works like a dream (can't speak for Tomtom or iGo
Landscape is really landscape - quite honestly, when I switch to landscape I get a real landscape feel - I usually to opt to run the unit in landscape anytime I get into my car and it performs fantastic
OEM vs OEM speed - out of the box the TP2 is just faster and smoother - don't ask me why - I do not know - it just is. Just this can be overcome with some tools / custom ROMs for the TP but truth is in the pudding here on speed and the TP2 wins
Touchflo 2.1 and beyond, the way it was meant to be - I'm back on the screen again but the space on a TP feel cramped and way out of place with a TP 2.1 ROM... a TP 2.5 ROM looks even more dorky... there just isn't enough space on the screen to get things done. Segments are cut off where they shouldn't be - the TP 2.1+ experience is obviously optimized for a 800x480 screen.
Productivity - again... more space = more room to view and use. I can type out an email and have enough space on the screen to not have to either a.) put the font down to small or b.) make the font large enough to see but get like 5 works on the screen per line. 640x480 on a smaller screen is just not good enough IMHO.
Keyboard - not even in the same realm. The keys are spaced out naturally. The device begs for you to use the keyboard - so simple, so clean, so... well just RIGHT. With the TP the keys felt smashed together (albeit you can type on the TP) you just don't get the same experience
Onscreen keyboard - back to the screen AGAIN - bigger screen = larger onscreen keyboard... I can now use the onscreen keyboard and have space to actually SEE what's going on versus get the sliver of space I was getting with the TP
Speaker phone - I cannot express how nice it is to be on the phone - put it face down and you have a GRADE A speaker phone. Not a tin can but a SPEAKER PHONE with noise reduction. There is absolutely no comparison - it just sounds better
Speakers in general - in the morning you'll catch me singing in the shower... why? Well because all my Zune subscription content is synched with my TP2 and the speaker on the phone actually sounds OKAY for music. Yes, I know, not the booming house system but it is PERFECT for a quick listen! It works well and I can actually hear a bit of bass in the music (I kid you not.) NO it's not BASS that makes the house quake but it is bass none the less.
Sensor - unit goes to my face... screen goes off... unit comes off my face.... screen comes on... so easy... so necessary...
These are just some of the reasons why the TP2 is a worthy upgrade. It made sense for me and I will never go back (I sold my TP yesterday for that matter lol.)