To gauge the worth I usually see what other folks are asking. You’ll have to gauge any sentimental value against the cost of restoration. My motto is buy the best you can and spend less money and time on restoration. An Alpine is the type of car you own because you enjoy it. If you want a restoration project, your uncle’s looks good as long as it has all the parts.
I question the value of the hardtop, since its been modified, and its hard to see what it needs to be un-done.

Here are some craigslist adverts to compare against, varying condition.

series 2 comparable, asking $2700

call this guy, looks pretty good condition. You’ll spend more restoring your uncle’s.

presentable series 5, more common, and presumably runs and drives $2200

See if that generates some discussion….