do I always root for underdogs?

It's a curious thing.  I finally pick up a really nice lens, then begin speculating about the next one.  I'll consider many factors, some which strike the average shooter as mildly to wildly irrelevant - and then overlook the most popular option while straining to find that ideal-for-me lens.

My Next Lens should be a very good wide-normal zoom lens that doesn't weigh a ton but fits nicely with the DA* 50-135mm.   I'm in no rush as I own the DA 18-55.. but many 'better' options exist.  Four 17-70 models, several third-party 18-50s and fast 17-50 f/2.8s, the old reliable DA16-45 and the new wide-ranging DA16-85 make the list alongside the DA* 16-50 and LimiZoom 20-40.  The Sigmas are odd in that half of them zoom in clockwise while the other half switch directions - so it would be nice to find one that turns the same way as the DA* (that knocks the list down a bit).  And hey why not use 67mm filters like the DA* as well?  That narrows the field to just a few.

image from dxomark.com

Oddly enough, one of the remaining items is a lens that has received constant praise for at least five years: Tamron's 17-50 f/2.8.  I've tried everything I can afford in that range except this lens (and the newer Sigma 17-50 that zooms 'backwards').  I've read about the excellent image quality, the field curvature that affects wide shots at fast apertures, the fact that over half the owners use the term 'workhorse' - yet I always grabbed another DA16-45 or 18-55 when the need arose.

The Tamrons are now below $250 fairly often on the used market, just above the DA16-45.  It has every feature I'd like except weather seals: range, speed, price, even matching zoom twist!  It does not have silent focus like the Sigma HSM and the DA*16-50 HSM, or the DC-motorized 20-40Ltd or 18-50RE.. bummer.  Is it worth paying quite a bit more for the first two, or essentially matching the 18-55wr for more money?

EDIT/ P.S. -  and the very next day reconditioned Pentax 17-70 lenses dropped to $230ish.  That too is a curious thing -- and one that blows all previous analyses to pieces.  I sorta liked the DA17-70 with its range, fixed f/4  and 67mm filters.  I didn't like three things: SDM only (which is bad if he ever-maligned SDM were to fail), no weather seals, and close to $500 so outgunned by Sigma 17-70s and the Tamron 17-50.  Until it's not!

image & review via
PentaxForums.com

So the 20-40WR is about 3x this price, the Sigmas 2x and only the Tamron (used)  can stay with it - less range but f/2.8 speed.  Thanks to the well-noted SDM fears the DA17-70 might even be the ultimate underdog of this lens type!  It's the lowest-rated DA zoom at PKForums other than the almost-free original version of the kit 18-55, mostly for SDM and other focus breakdowns.  

Two questions remain: did their reconditioning solve anything SDM-wise, we wonders?  And is $230 too much for a manual-focus lens not labeled "Samyang"?

Decisions suck.