if you have working familiarity with acrobat, illustrator and photoshop you've encountered 3 of the most difficult to master adobe programs already.
there's no overkill in subscribing to the entire suite. almost no one is an expert in all the programs and very few people (i believe) use all the programs in the suite. most of us use two or three heavily (and therefore develop expertise) and another one or two occasionally.
i believe everyone starts like you. occasionally using one program. then using it more and more and gaining expertise and then find the need to use another program in the suite and start learning it. i don't think it makes sense to learn anything about programs that you foresee no need to use. on the other hand, it is useful to know what the various programs can do so if the need arises you know which tool to use (and start to learn how to use it).
Thank you for the prompt reply and sharing your expertise, this is most helpful.