Not really a cheat, but you can pump your characters' stats for as
long as you have the patience at a couple of spots.

With Sharline, there is a plant critter that appears near the first
crystal she sees. Kill it and it drops a Blue Fruit, every time (along
with cash, usually).  The Blue Fruit allows you to spread five
points among your stats.  Go through the crystal to the shop (to
get the screen to reset), and return.  The same critter will be
there, and killing him will again get you a fruit.

Darius has at least one similar spot (that I have found), but requires
more work to get pull off.  In the upper shrine, in the far east
corridor is a Rock Golem.  Killing him seems to drop a Red Fruit
(twice as good as the Blue) each time he's killed.  You still
have to reset the screen with a visit to the shop, which is far off,
but it can be done. The limit to stat increases from fruit is 200 for
each. Darius' early Blue Fruit creature is the Paraday near the
fountain.