He's had a nice spring hardcourt run after winning a round at the AO -- SFs in Memphis; SFs in Delray Beach (finally coming through vs. Karlovic who has beat him multiple times); winning a round at the 500 in Acapulco. This may not sound incredible, but it's the type of run that journeymen (which he clearly is at this point) like Donald need to make money and maintain a ranking good enough for auto-entry into Slams.
I still hold out hope that he can win an ATP title (most likely a 250) before he retires. Memphis was a good opportunity as he beat Isner and played Harrison in the SFs and lost (who he has beaten multiple times before but who is actually ranked higher than DY right now and playing well).
As we've seen so much these days, players really seem to come into their own much later now. He's only 27, and doesn't seem injury-prone, so he could have a number of good years left.