Its great lens and a great focal length. I own it and love it. If you bought it i doubt you would regret it.
What do you shoot more landscapes/street, or portraits?
For landscape and street, it is probably my favorite walk around lens that I always have with me in addition to my DA* 55mm and FA 77mm limited. If I feel like working with another kit lineup one of the other two lenses get dumped, rarely does the 21mm
If portraits then with your lineup I would also consider the DA* 55mm or the new DA 50mm. Those would address the gap between 35mm and 70mm you have and they are excellent portrait lengths. (I can vouch for the DA* personally)
The 21mm it is sharp, small and a lot of fun