I'll wholeheartedly concede that it is too early to know whether the Astros made a big mistake in letting Wigginton go. But it's still fun to ask the question now, even though the sample size is too small.
Let's look at Ty Wigginton's offensive stats so far with Baltimore:
BA .216 OBP .256, SLG .270 OPS .526
Sheesh, that's bad. Really bad.
The Astros have settled on the two headed platoon of Blum and Keppinger. Here is the Astros' production out of 3d base, from Baseball Reference.com.
BA .364 OBP .432 SLG .455 OPS .886 OPS+ 133
The 133 OPS+ is the highest for any position on the Astros. Blum's OPS is .777 and Keppinger's OPS is 1.15. Sure, Kepp's numbers are likely to come down to earth at some point, but still I think the overall excellent offensive result demonstrates the benefit of a good platoon.
The defensive side of this comparison also comes out on the Astros' side. This is less surprising, because Wigginton isn't a very good fielder. The UZR defensive numbers can be exagerrated at this point of the season, due to sample size. However, setting that nicety aside, let's look at Wiggy's 2009 UZR/150 (extrapolated to 150 games) at 3d base compared to Keppinger's and Blum's.
Wigginton UZR/150 -27.9
Keppinger UZR/150 +30.3
Blum (UZR/150) +35.9
And I better give you a big caution on Keppinger's UZR, which is based on only appearing in 7 games at 3d base, meaning don't read too much into it. Blum has always been very good defensively at 3d base, so his UZR result isn't overly surprising.
So far this season, the Astros have gotten both better offensive and defensive production at 3d base, compared to Wigginton. So far, the Astros' decision looks pretty good.