Just my opinion but I don't believe miles really matter as long as you know the maintenance history of the vehicle in question. My daily driver is a 1999 F-350 Powerstroke with 6-speed manual transmission. I purchased it with 180k miles from a ranch that used it to haul horses across the country for showing. It was all highway miles. It now has 348k and still runs great. I have had to do the usual water, hoses, brakes, and HPOP, but all minor stuff relatively speaking. I replaced the clutch at 297k because the throw out bearing finally kicked the bucket, and rebuilt the trans at 324k because I overloaded the truck and trailer when moving from UT to TX (I slowly turned my 6-speed into a 5-speed over the 1500 mile trip). Then again I can't complain about a tranny going for something I did at +324k miles. As long as you take care of it, or know the previous owner(s) stayed on top of maintenance you should be fine. Even a major repair here and there is still cheaper than a car payment, or depreciation on a new car purchase. That being said its always a good idea to have a savings fund that you're constantly adding to for the big items such as engine, transmission, or driveline replacement parts. Do I hope my 7.3 powerstroke hits 1 million miles? Yes, that's the goal, however we all know anything mechanical can break at any moment and if you're prepared for when that happens with new parts of the funds to replace major components your set.
I work in the aviation world and the key to longevity is staying on top of routine maintenance. It does cost a few extra $$$ to replace something at the first signs of real wear and tear, but it always works out better than the "I'll fix that later" approach. That one always comes back to bite you in the rear when you're (insert adventure location here) and no where close to a parts store. It's very comforting in the back country not having to doubt your rig or equiptment because you personally know the history of all accessories and components installed.