Our B8 A4 is approaching 4 years and as of this year I'm doing all servicing myself including the S-Tronic (DSG) service as I have all the tools inc VCDS.
Honestly, I would much rather DIY and know it is done 100% correct than pay someone (dealer or indi) and be unsure if they have done everything needed or if it's been done correctly, or if they have lost the fasteners for the under tray and it's held on with 1 or 2 less than it should be, etc.
Personally I would MUCH rather buy from someone who has DIY'd and got stacks of receipts and clearly shown a lot of love for their car than from someone who has little more than a book full of dealer stamps and just looks at it as a machine that gets them from A to B.
As for resale value....remember, you bought it for YOU, not for the next owner! Do what YOU want, the car will sell regardless. Also, if you save £2000 in servicing then who cars if it sells for £2000 less than a car with FASH, it averages out in the end and you at least know it's all been done properly in your ownership.
If you DIY you will save even more, but it will not reduce resale value any more than going to an indi, just use decent parts / oils and keep all receipts to prove it.
I also got a blank Audi service book and have a "Self Service To Manufacturers Spec" stamp already, so I will be stamping the book, ticking the relevant boxes, noting the mileage and keeping all receipts on our car. Any future owner can't ask for much more than that. It's will provide them with more info than the Audi or Indi service history as to how the car has been looked after.