It seems you're asking a couple of different questions.
First - a board certified pharmacist in a speciality will have more professional opportunities & may indeed command somewhat more money than one who is not, within the same job positions they might each be qualified for.
However, if you are asking about become board certified in ambulatory care - at this point in time, it is my opinion that you will not be paid more than another retail pharmacist. BUT - I firmly believe that in the future, your job opportunities will in fact be differerent, which seems to be what you are alluding to in your post (not impressed with the lack of knowledge).
Now - in the future, will there be pay differences? Hmmm - I really don't know about that. If the past is any predictor of the future, no. If you look back on the experience of "clinical" pharmacy (can I mention AGAIN how much I HATE that phrase???)....when we began this grand experiment in the late 60s & early 70s...this same discussion ensued. But, over decades, what actually happened, was the education of ALL pharmacists came up to that which was required of those with clinical skills.
I think the same possibility might exist for ambulatory care/retail in the future. If you don't go ahead & get further education (which board certification reflects), you'll end up checking automated fills or doing mail order - something along those lines - jobs in which you won't be getting a pt in trouble by advising that which you're not experienced in advising.
But - compensation reflects the need & the supply of that which is to be compensated. Currently, these MTM positions are not very widespread, so there are enough of them around to not required extra compensation.
We'll see - it might be all just looking in a crystal ball & seeing how the shadows shift. But, if you're young, have time & the ability to get more training while you're young with fewer financial obligations on you - I'd recommend getting it because you never know what might lie ahead.
Now...if you specifically want infectious disease - that is a more hospital or public health based field of pharmacy which is different than any of the above.
Good luck!