To give you some motivation, YMEN is coming up soon as it seems, so get that thing ready!  :D

And to maybe calm you. The Windows warning comes up when the S.M.A.R.T. trigger parameters are exceeded. That's what it is, a warning and a good point for planning on a new disc, but it does not necessarily mean that you'll lose her in the next second.

This stuff is a self-diagnose way of getting an overview on the health of the drive. If e. g. the spinup time exceeds a certain level, it will warn you because there is a chance that the little motor develops a problem.
Same goes for the amount of faulty 'areas' on the drive. Some are ok and normal, some more trigger the warning, but the rest may well be perfectly ok (to backup).
As said, that tool will show you the 'red level' values, where the Windows popup just gives are general warning.