The price of the Arrow pipes is ridiculous at $1,887 plus 2 or 3 hours to fit them, so well over $2 grand. I saw a TE a couple of weeks ago that had the twin black Barratts fitted and it looked and sounded nice, but no separate ECU. I think the owner said they cost around $700. I went straight from the standard pipes with no power up kit to the Arrows, so don't know how much of the increased performance is attributable to the pipes themselves, but the dealer estimated plenty. What I can say is that the performance difference before and after the pipes was pronounced, throughout the rev range.
I haven't bothered changing the air filter, as I don't ride in really dusty conditions like those blokes do. I could be wrong, but I don't think the Unifilter adds to performance in terms of increased power, just better engine protection (the dust in the Australian outback is incredible).
I had the dealer fit all my accessories at the outset, including bar risers, as I'm 6'4" tall, so I don't know how much work is involved in fitting them. I kept the standard bars and everything feels just right to me.
The gearing change I did was drop one tooth on the CS, i.e. to a 14, as I do some tighter offroad work. First is now low enough to idle along at quite a low speed, and second is now much more useable as well. Before the change I was quite often in first in the tight sections, and second was simply too tall, particularly with the engine in standard form where it had little useable power below 4,000rpm. The combination of the lower gearing and much crisper power delivery from low revs has made it a far, far better bike offroad. The compromise of course is that it has lost some of its long legged nature on road. I can still cruise comfortably all day at 110-120kmh, but it is certainly busier than before. My feeling is that with the Arrow pipes it would easily pull the original gearing, so it comes down to the type of riding you do. If you regularly ride difficult, offroad work I would definately go with the 14, but if its mostly onroad or big trips I would stay with the 15.
My rear Karoo is pretty much shot at 2,400kms and I won't fit them again. They are good on road (smooth & quiet) and reasonable off, but they have a really low block that looks only just even from new and starts to look ordinary within a few hundred kms. I will go for either Dunlop D606s, which I had on my previous bike (2009 DRZ400E), or more likley Pirelli MT21s, which I haven't tried before. The 606s are good offroad, but howl a bit on.
Overall I am very happy with the bike. The only other mods I would like to do are fit radiator guards and Pivot Pegs. I would also like the tank to be around the 16 litre mark, but unfortunately there is no option available that I am aware of (the Safari being 25 litres, which I am not interested in).