Interesting choice - I narrowed it down to A and C. The rest can readily be eliminated:
B) Even if they did not have impact in the past, does not mean that their "future value" will not be impacted. This does not weaken the argument, it is a "psuedo-weakner" trap.
D) This does not weaken the argument of the counter-party. Even if this were the case, how does it solve the problem of the alleged unused space? Sure, property values could increase but it does not tell us if this is enough to off the "loss of business" that the counter-party is arguing for.
E) Not really relevant to the argument. The conclusion is mainly focused on the idea that the usage of the land will lead to a harm in the economy, because the opportunity cost of the land is very high. Employment is not really a consideration.
A vs C:
This was tricky. The idea of C is a sneaky one: If it is marked for public use, one could make the argument that businesses could not be built there, therefore there was never a loss. However, this is not actually weakening. It could very well be the case that, even though the land is marked for public use, the land itself could still be more efficiently allocated for a business, rather than a public use. So C fails.
A works, and it works well:
If there are businesses that are constructed with the park, and the park will also attract more visitors (implying more clients), then the land is actually used for new businesses - it is not just the "empty space" of a park, but rather there are businesses that will be placed with it, so the counter-party argument falls apart.
Good question I think
bb.