My opinion and what I did when I was racing my own.
AS long as it is making good power, has good oil pressure, and good leak down keep running it. Why fix what isn't broken.
If you don't have a good leak down guage buy the single guage leak down testor for Moroso ot the one I use from SnapOn Tools. IT is more repeatable in my opinion no matter were your air pressure is. Those that use two gueages have to be fed with the same air pressure or they are not as repeatable.
I liked to do lots of between rounds checks, like checking valve lash, checking carbs to be sure everything was working right, and checking under car for loose bolts or anything I could find wrong. My engines lasted several years, so I guess that means several hundred passes. Finding the little things going bad before they do damage goes a very long way.
Check valve springs all the time with an on the head pressure testor. If one gets 20 to 30 lbs weaker than all the rest get it out of there.
I highly recommend and also sell the best oil filtration system availaible, from Pure-Power.
www.gopurepower.com This makes for quick and easy oil and filter inspection between rounds and it is easy to clean. Costs lots more but you buy it one time only.
I have customers that run their engines for years and others with high horsepower that bring them back at the end of the season for freshening.
Some of how long you can run it will depend on your engine builder but a whole lot of it will depend on you and how much you stay on top of preventive maintenance.
Ed