1)
Spurious autocorrelation of non-synchronous trading data was analyzed in this article: http://www.amazon.com/An-econometric-analysis-nonsynchronous-trading/dp/1245789457
During some time intervals a lot of trades occur and during some nothing happens(so prices are stale). So serial correlation of traded prices may be present but this may be due to stale prices.
See this paper for an example when prices are generated by a stochastic drift and measured with non-synchronous traded prices: http://eml.berkeley.edu/~anderson/Sources-042212.pdf
They also proposed a way to compute autocorrelation without this bias: eliminate NT by computing returns over disjoint return subperiods, separated by a trade.
2)
Discreteness introduces large kurtosis since most of the price moves are one tick up/down for liquid securities. If the "fair" price has to move 1.6 ticks away, due to discreteness it has to move 2 ticks.