I think including the rows above and below should be fine. Thats what I would expect a new player would think when they see "adjacent".
If you do redefine it, you should probably add in that explanation to the card text for clarity.
For most of the spells in the game I think this would be a pretty nice addition.
I would say its on the pricey side, except that there are a few spells where the combo's potential would warrant needing a high cost.
-Mitosis
-PU; Massive SoW-Wyvern-Sky-Blitz OTK anyone!? ( *cowers in fear from this combo's potential OPness* )
-Immolation; just think of the pheonix and spark abuse
I like some of the combo potentials, but PU seems like it will be OPsville for sure. Not sure how to fix that.