Yes, in the case of Youk and Lowell, Youk is more valuable offensively due to similar OPS but higher OBP for Youk. I meant in the general sense don't discount SLG. It does correlate higher to runs scored, and due to it being on a 4.000 scale, the variance is larger, meaning fewer small differentials when upgrading the SLG at a position.
So, Youk would produce a higher VORP at 3B. Lowell was good for 77 EqR, and Youk was good for 85. However, Youk was only 4 runs above average at 1B, while Lowell was 18 runs above average at 3B. I suspect Youk would be about average at 3B, which makes Lowell about 1 win (10 total runs) better.
My point about showing the importance of SLG was that Youk plays a corner spot. That is where you find your SLG, and Youk just doesn't bring it. A .800-ish OPS just isn't enough from 3B, IMO, and it isn't anywhere near good enough at 1B. Youk has already hit prime age, so increases in power are possible, but unlikely. That is why I don't consider him a long-term answer at that position, so, since he hase more value due to salary, he is who I would move.