@Avery - If you take a look at Ruckus's most recent
EoL/EoD doc, life cycle cadence seems to be about 2 to 3 years. The R500 was EOL'd 10/2018, so I wouldn't be surprised to see the R510 hit the chopping block in the next few weeks or months. From that point forward, another 1.5 to 2 years of software support, then three more years of security-only updates, before dropping support altogether. So from release date, usually around 4-5 years of software support, 7-8 years of security patches, before full EoL. Just about par for the course in the enterprise space; perhaps not the best (Cisco or Aruba may be better at times), but definitely better than many SMB vendors and almost any consumer brand.
As for analogous models, the newer versions at the medium tier would be the R520 and R550. There are five series (tiers): 300, 500, 600, 700 and 800, numbered roughly according to the amount of client density and range they're designed for. Historically, 700 and 500 series have been the most popular to deploy, so the bulk of eBay stock will be those. The R710 has a cult-like status (coming from the 7982\R700 design which made big waves). Like the R510, it will probably reach EoL at the same time. To go for longer support, you'll need to bump up to a _20, _30 or _50 suffix model, but you'll of course pay a premium in doing so.
One item you must keep in check when going up-series/suffix with Ruckus (or any AP vendor for that matter) is power draw. For example, the R720 requires a minimum of UPoE or PoE++ (802.3bt) in order to broadcast at max power. Otherwise, it will run at only partial power, reducing its performance, and consequently, you may have better off just buying a model that could run at full power on 802.3at, if that's all your switching and/or injectors provide for. So it's not just the cost of the AP itself, it's also the implications that it puts on your power budget and PSE hardware cost.
Hope that helps.
@coxhaus - Yeah the 720 is quite a nice unit. I run one at home. It massacres neighboring RF interference without batting an eyelash. But for ~$700 each street price, I would hope so.