I think that this would be nice, but as many of us know, the best plan for one set of parameter values for a query is not always the best plan when the parameters values, so you may not actually get the best plan for your application. Now if this worked off of a workload file created using a trace where the optimization process takes into account the parameter values provided for each query in the workload and produces the best plan for that workload. So if you have a query where you are selecting customers by country, the optimizer takes into account that 60% of the time the query is for customers in the US, then you might have something.

Something I think is somewhat related, I'd love for MS to allow you to tell Developer Edition what mode to run in, i.e. Standard Edition/Workgroup/Enterprise, so I could be sure I'm not developing something using Enterprise only features when my production server is Standard. This might be something you need to select when you install.