X heads on 318

When I purchased my barracuda, it came with a standard bore 318 with X heads and intake manifold from a 340. This car will never hit the strip, so I don't need to make crazy power, but I would like a little more HP than a standard 318. Does it make more sense (cost-wise and performance-wise) to buy a set of 302 or magnum heads and sell the X heads, or keep what I have and try to increase compression with flat-top pistons, milling the deck, etc.?