A tune improves your overall performance and drivability.
Granted your "peak" numbers wont be alot higher but your power under the curve will greatly improve.
For example on an SVT you only get around 8wtq more at peak.... but in the lower rpms you make almost 30wtq more than stock.
[B]1951 McCormick FARMALL M
2007 MINI Cooper S Turbo... new project car
1998 Chevy 3500 Ext cab, long bed, 4x4, duelly, turbo diesel
2004 Harley V-Rod.... sex on wheels
2011 Harley Electra Glide Ultra Limited