Eh... ashes and embers have actual content -- the base thing just enables donator features, which other than the item vault (which can be helpful starting new characters or specialized builds, but is entirely unnecessary) and early access to possessors is entirely cosmetic.
Of the DLCs themselves, embers involves significantly more content. Ashes is a couple new classes, a race, some artifacts and enemies, and only one or two new areas and a passel of lore, the last added on to the main campaign. Embers is an entire new campaign (that's notably better constructed than the main, imo, especially from a lore perspective), three new classes, three new races, what amounts to a crafting system for item attachments, and a bucketload of new artifacts, on top of whatever else I'm forgetting. I'm not sure how awesome I'd call it (I certainly enjoy it quite a bit, myself, but awesome is rather subjective, heh), but it's definitely the better DLC by a pretty significant margin.
Not sure if getting just the DLCs open up donator content for you, unfortunately, though it doesn't look like it'd be something of a workaround on the steam version anyway. I'd probably recommend nabbing the 4.80 1-3 thing, if you were going to get dlcs. If you're not interested in either, or playing the thing on steam, you might be able to open up just donator stuff even cheaper just donating directly. Forget what the minimum donation is, if there is one.
E: Ah, yeah, had forgotten that... basically, my stance on the DLCs and donator status, is it's arguable enough it's worth the money just for that, that I probably wouldn't directly recommend them for their content. It's mostly pretty good content, just maybe not dosh good content. However, if you've enjoyed playing the game, and want to send T4/DG some monetary kudos for the good work, it's a pretty great way to do it and you get some nice extras for giving a project you enjoy a bit of money. So don't look at it as a question of whether they're worth the price, look at it as a question of whether you think floating the dev the cost is something you think worthwhile. If it is, then get them as a way to donate, and consider the added content a nice extra rather than your primary goal.