variation... ie don't be repetitive. Use more than one tile, use lots of different tiles.

You could look into aperiodic tiling. You can generate sets of tiles that can be placed in non-repeating sequences.

that looks v.handy - but even in the examples shown you could not repeat it seamlessly if i understood correctly.

You don't understand: nothing is simply "repeated", Stam's ingenious substitution rule is simply a way to compute cheaply which of the 16 Wang tiles you want to place in each position of an arbitrarily large grid. All tiles match seamlessly with the other tiles that have the same edge type (for example yellow vertical: either of #1 and #15 can fit left of #13, #14 or #15) because they have been drawn that way.

There are simpler ways to lay out Wang tiles and corner tiles; for example you could have one or more tiles for each arrangement of four edge or corner types, assign all of them pseudorandomly (applying a "noise function" to edge/corner positions) and choose (again, with a pseudorandom function) a tile variation for each location among the suitable ones. Something of this sort, with only two corner labels, is done in an article of GPU Gems 1 or 2; they arrange tiles in a square texture according to a de Bruijn array so that the texture itself doesn't have discontinuities and simple wrapped texture lookup can be used.

Draw maybe 2-3 different tiles per map. Not including corners/sides of wall.