That plane has enough equipment to get your IR in. It's got enough equipment for basic IFR work. It has more than enough to be a great VFR airplane.
One inexpensive upgrade if you wanted to beef up the IFR capability would be a KNS80. It has VOR/ILS/DME/RNAV. You can score one of these for less than a stand-alone DME box and in this case, it adds a full featured second NAV, DME and it lets you file /I so you can at least get a direct enroute sometimes. You can probably get one and indicator installed for $2000.
You could also add a KLN89B to the KMD150 and have a pretty nice IFR GPS solution.
I'd have to see the plane in person, but it has the look of a well-cared for plane. P&I is less than 3 years old and they didn't "cheap out". The equipment is certainly nice, all King, all good quality.
One thing I'll say as an owner: NICE airplanes are very rare do not be afraid to pay a premium for a NICE plane. They also don't last on the market too long. If you stumble upon a really nice, well cared-for plane, consider yourself lucky. I'm not saying this one is, no way to tell except to look.