DSG will only speed up the first harvest for Ancient Fruit, or any other multi-harvest crop. It won't reduce the time to second and subsequent harvests, so probably only worth the effort to use DSG on crops you need to replant
On the other hand, Fertilizer and Quality Fertilizer will provide benefit for second and subsequent harvests of Ancient Fruit, so if you're not processing it all, these are definitely worth the effort
DSG will only speed up the growth stage, not the multi-harvest stage, but given that growth stage is (without other modifiers) a full month, it shaves almost an entire week off of the initial iteration. If you're starting with only one or two seeds and using a Seed Maker to propagate, using DSG during your initial growth stage can significantly speed up how fast you fill your greenhouse, shaving entire seasons off the time to completion. So yes, it has zero benefit for you after the greenhouse is fully propagated, but it can help you get to that position much more rapidly. Meanwhile, Ancient Fruits are just *made* for kegging, as the growth and processing times are synced up so well, so it makes zero sense to have a greenhouse full of ancient fruit and not turn it all into wine, at least if profits are your concern.
Postgame, the Deluxe Retaining Soil can save you some space by replacing the sprinklers with more crops, which makes it effectively the only 'fertilizer' that has a mechanical benefit after you have finished filling the greenhouse.
So I suppose the only real question is: Do you value getting your greenhouse filled faster, or do you value maximum capacity more?