For me personally there's three "categories" of upgrade:

1) Above-and-beyond upgrade; e.g. specialty suite or villa, especially if upgraded from a base room
2) True upgrade; e.g. meaningfully larger room, (junior) suite or for resort properties where sea view is at a significant price premium I'd count that as well
3) Technically an upgrade; the "high floor", "club room" (if no other benefits) type of upgrade

Generally, I'd say I expect 2), am very happy if given 1) and somewhat disappointed if given 3). In my experience, IHG skews more towards 1) and 2), Marriott and Hilton towards 3).