Its a simple choice, either pay for repairs or pay depreciation and monthly repayments.

You will have to buy tyres whatever car you drive.

Slow down and save money. 25,000 miles @ 45 mpg will cost you £852 less than it will at 36 mpg. That will almost pay for your repairs.

70 mph is the legal limit, drive at higher speeds and risk a fine, points and eventually a ban if you get caught enough times.

Keep your current car until it dies. You obviously like it. Something new and similar would be approx. £30k. Yet with your mileage a new car now would be almost valueless in 5 years, like your current car. The odd £1,000 repair bill is nothing compared to the depreciation you will suffer on a new car.

Even if a new car were slightly more economical, it wouldnt be enough to cover the extra cost of buying it.

..... has been bit expensive with 1K repair each year at least and change of tyres

Interesting - what has cost £5k over the last 5yrs?

If you cruise at an indicated 80 [a true 77ish] so prob safe from all the gantry cameras an extra 4psi might be beneficial for both economy and tyre wear. I have just changed a set at 40K plus - they were still legal.

That's p1$$ poor economy from a diesel - unless you're driving "flat" most of the time.

I have a Saab 9-3 Aero 2.0T with a Maptun tune to 255PS/360Nm. About the same size as your A4, but probably heavier at 1625Kg and running economy sapping 235/45/17 tyres. On my 45 mile each way commute I cruise at a steady 67 ish and get 42mpg. If I drop to 55, it goes up to around 50mpg and if I up to about 77 I still get 34-36mpg. If I hoof it about at 90+ it'll still do 30+. It takes a fast A+B road run, overtaking everything in sight at full pelt to drop it below 30 (indeed, it's hard to keep up such a pace on todays busy and scamera infested roads).

Cars cost good money to buy and depreciate even if you leave them in the garage. the longer you keep your car, the less per year it's costing you, even if it does need a few repairs (and does that cost include the service anyway?). If that £1k includes a set of tyres at 400-500 a set, then that's hardly expensive.