None of these lenses will outdo your Tamron 90 sharpness. I have all these lenses (
had the DA 35 macro) and the Tamron and it is hard to beat a dedicated long macro in sharpness across the frame.
I love the 70 for people photos. It's a fantastic, light, compact lens with a wonderful 'voice'. It is, however, the closes in FL to your 90, though much smaller.
The 40 is exceptional IMO for its focus speed and versatility. It is, however, very close in FL to the DA 35mm's. You would split hairs between the speed/sharpness/rendition of the 40's and 35's.
The DA 21 is an interesting lens because it is wide angle, and very compact. It is a lovely, versatile lens in a market where most wide are huge.
If I was in your shoes I would get the 21, simply because the 35/40 you have mostly covered already at great value and price
erformance. Wides are generally not sharpness demons so asking for it to out-perform a macro...not going to happen. The 21's strength is its perspective and versatility in a small package. The weakness of the APS sensor is wides and the 21 gets that done nicely.
The 70 is hard to pass up. If your shooting style is more towards a longer FL tele end of things, then I'd get the tele. That said, I use my Tamron 90 as a long tele/portrait lens a lot, so in your case it can do double duty. The knock on the Tamron is size and slow focusing. The 70 is much superior and has a better rendition IMO.
So if you're lacking a wide in the bag and want to travel light, the 21. If you're looking for a a tele-FL and portrait monster, the 70. Your DA 35/2.4 is not something I'd add to at or near the FL.
Good luck.