Not a bad idea.
A map for ideas, new tactics and fun :)
It could be like kind of a "god mode" since the tower placement here would be killing :P
yes could be nice with practise grounds, myself i probably wouldn't play it so much except if i get a "bright" idea i have to test coz i like to get exp ;) but could prove useful/fun on occasion, and others might enjoy it aswell and good place for newbie's to learn the game, though you already have the tutorial for that, but you still need some IRL experience to know what to do and what tower to put where to be efficient.
and if the practise grounds would become a reality there would be nice to have a 2x, 3x, 4x speed button so you dont spend 5-6 hours on a game that don't even give exp =)
peace //
