... is it something that I can accept or should I invest in 70D?
Unless you're a professional, a camera is never an investment. It never appreciates. It's an expense.
Depends on what and how you plan to shoot. If you think you'll be doing focus-critical work, like macro shooting, where you work with a tripod and manual focus, it's not at all critical, as you're bypassing the autofocus system altogether.
If you're planning on using supertelephoto lenses on fast-moving subjects and need the AF to nail focus each time, then it can be much more critical.
Canon 760D has a 24 mp crop sensor so exact focusing may be very important to avoid soft pictures,
This, in and of itself is not a factor that means you require AFMA. In fact, the majority of entry-level dSLRs that don't have AFMA have the same resolution, so a number of folks are apparently getting by just fine without it.
I use only original Canon lenses but change them very often, and as most of them have plastic mounts which may wear out over time, microcalibration may be a very important feature to have ...
Actually, what this is telling me is that you only own entry-level lenses (EF 50mm f/1.8 and the EF-S 18-55 kit are probably the only two lenses with plastic mount plates). In fact, nearly all lenses these days have plastic mounts. And if you end up with a lens/body combination that is so out of calibration you notice serious AF issues, you can always send that gear to Canon service and have them calibrate the gear for you (i.e., do the adjustment).
To my way of thinking, it's mostly a convenience feature, unless you a) are completely unwilling to send a lens/camera combination to Canon to have them calibrated, or b) have a large number of lenses, or c) do a lot of shooting where autofocus accuracy must be spot-on at all times, and d) shoot wide open with fast lenses all. the. time.
(there must be a reason that all upper line bodies offer it).
The main reason is that successful professionals who can earn enough to cover the cost of high-end gear tend to use high-end gear to make things easier on themselves and to save time. Better glass generally means less post-processing. Harder-wearing bodies can take more wear and tear. And having AMFA means you don't have to wait on Canon Service to do adjustments for you.
I shot with a 350D/XT for four years and never felt the need for AFMA. I also used that camera body to shoot birds with an EF 400mm f/5.6L USM. I never needed to send the combo into Canon for calibration. I now shoot with a 50D and 5DMkII, both of which have AFMA, and I've probably used the feature a grand total of twice, and it only helped in one instance, because my methodology of adjusting the AF calibration was less than optimal (it's why I happily use Magic Lantern's auto dot-tune feature).
Note that Michael said he only noticed he needed AFMA when he used a $2000 telephoto L lens. And note how I said I used an $1100 supertelephoto L and never really did. In my book, this is a gracenote/convenience feature; not a have to have, and not a great excuse to indulge in feature-greed. To me, Don't get a 70D just for AFMA. Because, frankly, you probably need the cash you'd save for better glass. And the 80D was just announced. :) The 70D's used price will probably be dropping soon...