Jessica is essentially correct. You are not really "covered" on your dad's side with just a Y-DNA test, which only applies to the paternal line. So you need an auDNA test for your dad.
Having the relatives further back, generationally, is a big advantage, so testing grandma is definitely a great move.
If you have tests for both your mom and your dad, all a test for yourself would add - genealogically - is to confirm that your parents are really your biological parents. I'd probably want to do it anyway, as something interesting/entertaining, but it's not critical if you have tests for mom & dad. I'd say yes, if there's a limited pot of money for this right now, that it would be better spent doing your wife's parents vs doing yours (or even hers!). I'd add that upgrading to Y-DNA111 isn't likely to tell you all that much beyond what Y-DNA67 already tells you, but it costs a lot, so I wouldn't make that a priority either.
As far as saving money goes, you could have just done AncestryDNA for grandma, and then downloaded a copy, and uploaded the data to the other platforms. But you could have other interests besides - the medical info some offer, for example.
You can also put your data on GEDmatch, a free site where it can be compared to people from other sites, at the chromosomal level. For real genealogy, it's all about the DNA matches, so you want to be able to match against as many other people as possible.