For what you have for £1600 initial price, I don't think you messed up at all. I payed about £100 more for a bike with almost 8k more miles. Sure it was in brilliant condition, had brand new tyres (bollocks dunlop cheapo ones to be fair) and brand new OEM carb to engine rubbers but If I'm honest I probably paid too much. However, I don't regret it at all. I have had the urge for all sorts since buying the bike, big supermotos, TDM 850's, Teneres, pretty much anything with more leg room for my silly long legs and the same fun factor. To be honest though, a supermoto wouldn't have toured wales with my brother on the back anywhere near as good this year and when I go for a ride with my mates on their sports bikes, a TDM would be harder work to try and keep up with them. The Fazer has stunned me at just how good a do it all it genuinely is. THE BIGGEST OVERSIGHT for me was that physically, if you're over 6"2 with long legs you will get cramp or severe leg fatigue on this bike in standard setup. The same goes for your pillion.
My initial plan for this bike was to buy the best one as I could afford and keep it forever , initially as my main bike then if I can afford an upgrade in the future have it as my secondary commuter/ fun hack. I plan to still do that and have began modifying the bike to allow me to ride it in more comfort. I will be making a thread soon to show what I have done, I can send you all of the links and the company I have used for the seat upgrade to see if they can do the same for you. I love this bike, I didn't even realise at first but spending time off it then going back to it I just think what an absolute legend it is. It just does everything I need with ease and performs above and beyond its price tag. How tall is your wife because I went 150 miles from Torbay to Portstmouth with myself 6"4 and mate 6"2 on the back and it did it with ease and wasn't too horrific for either of us, we just had a fair few breaks at lyme regis and a few service stops. No bike is 100% comfortable unless you buy a goldwing, there will always be a compromise. As said before, think hard before you make any decision as at this time of year especially you are going to make a loss on a great bike.