Agree with all of the above... My ride today was pretty tame for off road. But here is the run down.
Loose soft new gravel
Hard pack old gravel dirt road
Rough seasonal access road
Soft moist dirt construction - slow speed
Rutted Dry hard mud sections
30 foot dirt pile and sharp 6 foot drops (steep enough for me to drag the bash plate over)
Qualifier/disclaimer: I have not been in any soft sand or major rocky terrain or deep mud. I have only spent two days riding the thing with this setup. I have never used the TKC's before so that might be tempering my judgement.
Report: The 21 inch shows little or no change on pavement - it is a bit slower but the losses in turn-in compared to the gains in dirt is no comparison. I was much more confident in the loose gravel and had fun roosting it up and sliding around - the front felt planted and did not feel like nosing in/plowing like the 19 did. Much more stable in faster loose gravel and transitions from side to side of road. In the soft stuff - trials like riding slow speed standing up the results are even more impressive. Rolling over the deep ruts and in and out of them was no problem.
Ralle-moto triple clamp.... without a doubt the biggest and most noticeable change up front and highly recommended. Very stable with both the 19 and 21. Makes all the difference in the world. One of my buddies questioned the fact the increased stiffness might take away some feel but I suggest the opposite is true.
TKC's: Gotta say my first pair and even with the narrow 90/90 front and 140 rear!!! They are incredible for what they are and even I dare say more confidence inspiring than the Heidenau's on pavement! - However I have not been in rain on them yet. They seem actually quieter and less vibration than the Scouts too - which is not tough. I will be putting my 19 inch set of wheels back on for a trip to WV soon so will be able to make a comparison.
Overal: Lots of money for sure - and you can do it for less and get the same gains with more inconvenience and less cool factor, by just adding the front 21 inch rim and switching your hardware over with no fender but... - the Woodys superlites are gorgeous and the whole set up is bling in the extreme but super tough and strong. The TKC's work very well and the Rallemoto triple clamp next to shocks is the best upgrade I have ever made.
If you have the money and feel like spending it, then this extra set of wheels is well worth it. It actually makes me feel like I have another bike or much broader options sitting in the garage taking up the space of only one bike.
My advice: Go for it.
Manxman - gotta get on the dirt my friend!!! Good luck. We had a nice long country ride today and it ended up 18c which in comparison to the snow we had two days ago is pretty awesome. Good luck.
As your attorney, I advise you to buy a motorcycle. How else can we cover a thing like this righteously?