I think the two best reasons to use Kevlar (or carbon fiber) in strip boats are because you want to and because it would look good. You can get some idea of how Kevlar affects the mechanical properties of a kayak on the strip lay-up page at the link below.

Sam

: I noticed that Nick had what looked like kevlar (golden yellow fibers) lining
: the inside of his Petrel. I am wondering about the pros and cons of lining
: the inside of a strip boat intended for rough waters with kevlar. How much
: weight does it add to a boat compared to fiberglass alone? Is it a pain to
: work with? How much strength does it add to the boats hull? What is the
: cost?

: It also occurred to me that the added strength kevlar lining might provide a
: stripper would only be useful in serious rock-gardening. If the boat could
: crack if one were landed violently on a rock, the helmet or cervical spine
: might not fare so well if one landed upside down.