I have many domains coming up for renewal with creation dates three or four years ago. Most are not great name since they have hyphens and/or are not dot coms.
For example, Automobile-Repair.net was created in 2006 and I never got around to putting a site on it...
Google's Kw Tool is showing decent volumes for the related searches to this domain words even in hyphenated format; and advertisers are paying a lot for the phrase.
While I am not an expert in domain valuation (and frankly, I believe a lot of domain valuations are overhyped with perhaps a small number of exceptions) I would not recommend relinquishing this particular one you mentioned in your example. Unless you want to sell it and, if that's the case, try to get as much as you can for it.
If only there is available resources, I can envisage the domain being developed to host a network of automobile repair shops, providing ratings of the good, the bad, the ones to avoid at all costs, etc. zSuch a site will also provide info and articles for DIY,..., and should eventually find a way to get featured on cartalk.com... Just imagining!!!
If renewal fees total amount is large and part of the doubt to renew or not to renew, you may want to transfer some of them now to a different registrar. First, some registrars are offering specials on transfers at this time. Second, this allows you to "renew" in chunks and rather than doing all renewals at the same time. This is why some people have recommended not to synchronize renewal dates.