He's probably going off the same info that many here are, ie that the time since the last refresh has been longer than average (which is an unreliable indicator for the reasons I stated earlier). I really doubt salespeople in the field have any inside info; if they did we'd see a ton of release date leaks like we do for other products that have to involve third parties in their release.
Again, if you actually have a need for a computer now, it's ridiculous to wait for a refresh if you don't know when or even if that refresh is coming. The reality of electronics shopping these days is that there is always a refresh coming in the near future, so you have to come to terms with the fact that your purchase is going to be obsolete early in its lifetime. If you're just buying it to buy it, then waiting might be a good idea though. I don't know which camp you're in.
I would say that very much depends on whether the present model is sufficient for your needs. I would say in the case of the Mini the present model doesn't fit the bill. For a start the meagre HD is not sufficient for my current data plus a Bootcamp partition for Windows. As there is no TB connector on the present model then that is a real issue. Also there is the issue of the C2D. I would wish to keep a Mini for a minimum of six years and consider the current C2D will be insufficient long before then.
Therefore if the choice as you see it is to go for a Mini now or don't go at all then I would have to choose the latter.