You should Scale your block, but I would easier if you create a feature and scale the feature (like a surface)
I think you'll need to Explode the Block first.
You'll also need to add constraints to the various splines to get 'sensible' results.
Do you want only the width to change and the height to stay the same? Do you want to maintain the same basic "look", so that the tangencies and curvature continuities that you have in your spline right now stay the same?
I notice you had set the splines to proportional. That forces each spline to maintain it's shape, so that it just scales in size or rotates as you move the end points. But, as you found out, SolidWorks has a hard time solving when you multiple connected proportional splines.
Tricky problem. I'm not sure how to solve it.