1. Apple still see it as a "hobby" and has gone as long as about 4 years between updates.
2. Even previous generation (even first generation) seems easy to sell in the used market after new versions come out. If you buy a refurb or about $85 now and a new one shows up in October, you might sell that refurb for about $65. That would be like renting full use of one for $2.50/month between now and then. If #1 applies and a new one waits until 2015, it would drive that rental-equivalent number right on down.
3. Consider being a buyer in that secondary market at $65 or so (craigslist, etc). Then, you might be able to fully enjoy one now and sell it for about $65 when the next one comes out- a free rental period if you will.
It's a very useful device (well beyond being a nice portal to Netflx). For $85-$100 with a seemingly strong second-hand market at around $65+, it seems like a no-brainer to get one when you want one.