"With Soil Appreciation II, tending a Patch takes half as much time AND more XP each time, plus more chance of extracting Loam from delicious Dirt Piles. What's more: this skill is also a must-have for several other handy skills. Go soil!"
You're missing a verb before "more XP each" unless you mean to say it "takes half as much XP", in which case the grammar is correct.
My suggestion: ...tending a Patch takes half as much time AND (gives/grants/generates) more XP each time, ...