+1 Heavy Spiked shield of Bashing plus Vital Stike = 4d6+1+(1/2 strength bonus)???
+1 Heavy Spiked shield of Bashing plus Vital Stike = 4d6+1+(1/2 strength bonus)???
That is indeed how the figure would look. Get Double Slice to bring that str bonus up to full.
Since you only take one attack with vital strike, you'd use your full strength bonus on the damage. Note that you can't take an off-hand attack with vital strike, so the shield bash is your only attack in this case.
The damage would be 2d6 base +1 enhancement + Str bonus +2d6 vital strike, with the vital strike portion not being doubled on a critical hit.