I think that it does change things quite a bit.
The reason the LT position is so important is obviously because it is a right handed QB's blind side. If you look at the talent in the league at DE, most of the pass rushing talent is concentrated on the right side (lined up against the LT). Examples of this are Taylor, Schobel, Freeney, Hugh Douglas, etc... Given the amount of pass-rush talent at the RDE spot, you need a superior pass protector watching the QB's blind side.
With a lefty, this is somewhat diminished. IMO, you don't need quite the level of pass-protection from your LT because he isn't comming from the blind side. Also given the stated drop in pass rushing talent at the LDE position, you don't need a LT calibur pass blocker at RT.
That's my take on it anyway. :D