You have to pick:

Since you're unable to tell the truth, you could use that to gain knowledge of the universe just by playing 20 questions. I think people would overlook my annoying habit of always lying if I fixed the worlds problems.

That is an interesting interpretation, although I would describe call what you are describing as "Be unable to say anything true". In other words, "telling the truth" is an expression that means "not lying". It DOESN'T necessarily mean saying what is absolutely true.

Suppose A is true but you think that A is false. I think it would be "telling the truth" to say that A is false, and lying (aka not "telling the truth") to say it is true. Even though it is in fact true in an absolute sense.

So I don't think this would give you any information about stuff you don't already know (or think you know).

Anyway, that is a lot of yammering about a minor point. I just don't want this option to artificially inflated in value.

Does this only compress your height?
After 1000 sneezes you'll be 36.77% of your original height. You'd start becoming very oddly-shaped if it didn't shrink all your dimensions.
Do the WYR Pixies magically make it possible for your body to function at extremely small sizes?

Your body stays at the same proportions and yes, the WYR pixies make you able to survive at tiny sizes.