Yep, been a long time since any ViP series box has been built, except for the ViP211Z (& it has no internal HDD). I'd guess even the last ViP922 came off the lines in 2011 MAYBE 2012.
Like TheKrell said, they can be quite reliable. I had a couple of original ViP722 DVRs for many years before moving up to HWS and only near the end did I start having minor problems (fan). Mine sat in the open atop laptop coolers. The ones sent thru refurb might not have had such care.
Is this your only receiver? Do you feed just the single TV? If so, the Hopper may be a bit of overkill, but as new, it will be more reliable. If you go this route, make sure it's a Hopper With Sling (HWS) and not the original Hopper. And get an EHD and transfer all your saved programs over so you can watch them on the Hopper.
I don't think any of the old ViP boxes can be said to be more reliable than the ViP722 series. Maybe you just need to keep trying until you get a more reliable one. But as they're all years old, they will all likely have years of wear on their HDDs. I suppose a few HDDs got replaced early in the program, but availability may have dried up and Dish probably just junks the one that have known bad HDDs today. Yes, there are plenty of 500GB HDDs out there, but are they of the particular models that the ViP722 series can accept?
Dish seems to want to move as many people to the Hopper series as possible, so they may make you a great offer, even free. To better consider your options, contact a DIRT team member here.
You might like some of the additional features of the Hoppers, such as transferring programs to tablets for offline viewing, and Dish Anywhere, that let's you watch live or saved programs on smart phones or tablets wirelessly over the Internet. And perhaps that third sat tuner will be of interest to you.
Please be sure and let us know how this all turns out for you.