Usefulness of 1080i releases?

In cataloguing my collection as a means of quickly knowing what I have and haven't yet acquired, resolution is one of the variables I make note of. While most movie releases are at best 2160p and most TV releases are at best 1080p (with those in 2160p having inconsistent season availability at that resolution), a fraction of my collection remains below that, usually at 480p or 720p. While not much can be done for 480p content without the studios themselves rescanning them at a higher resolution, it seems that some 720p releases alternatively have 1080i releases less-commonly available as well. Assuming both resolutions are available, is there a feasible way to convert 1080i releases to a distortion-free 1080p equivalent, or is sticking with 720p the better option?