Interesting point - but I always assumed that cheap inks also have drawbacks with regards to longevity, resistance to sunlight etc.
OEM inks are not as trumped up as you think they are. Epson and Canon make it seem so because it's in their interests to protect the HUGE margins they make on it.
The are a lot of crap inks out there, don't get me wrong. But the best ones are not hard to find, and perform even better than OEM (in terms of color gamut for the most part). And they save you heaps of money - the best ones don't even cost a quarter of OEM. Guilt-free color-lab quality prints that costs pennies, yeah baby. It's quite addicting actually.
In fact, it is the same OEM ink manufacturers that make the the top of the line refill inks.
Essentially what this all means is that for any non-professional (or for me, at least) it is simply impossible to get great prints without investing a lot more money and a lot more time. Both of which I am able to invest only to a certain extent. It just looks like I have to reduce my expectations, and that frustrates me.
It actually depends what your definition of great prints are. In my opinion, what you're getting is already great - in comparison to what most people not using LR/Photoshop, icc profiles, and professional home printers get.
But it seems what you want is the peak of Mt. Everest, which means you do have to invest time and money to reach. Nothing comes easy my friend, such is the bitch called Color Management. So I say take the plunge, get a spectro. Best investment you'll ever make.