I remember shooting the K20 when the K5 came out with its great Dynamic Range, ISO 80 and low noise - it was calling. Its initial price was $1700. To me the K5 with the sensor was the watershed product for Pentax. After about 18 months, its price dipped down to $750 for a day and I called to order one. That was a bit over 2 years ago. With the K20's sensor just getting nosier by the shot, it was the right move.
In reading about the K3, it appears to be a wonderful camera. For whatever reason, the K5IIs appeals to me more. However, my current K5 is going strong, and I really have no urge or real need to upgrade.
Having said all of that - it is your question, and only you can truly answer it, based on your perceived needs, wants and desires. I would ask myself a couple of questions...
- What would a K3/K5IIs allow you to do that you can't do now?
- What would a K3/K5IIs make it easier for you to do that its pretty difficult to do now?