We have been paying for manta pro since last July and I will give this feed back.

1. Your "List Views" will definitely go up with a paid vs non-paid listing our went up about 4 fold.
2. This seem to help you get for your sales and service items when a customer is doing local search for example we organically ranked for "my service my town" but not "my service neighboring town"  adding pro listing made it so we were first page for the area local search.  Please not this is a niche industrial market we are in.
3. According to Google analytics I receive maybe one site visit for every 40 listing views.  I cannot say how many call as we cannot afford call tracking currently.
4. We run PPC campaigns, so form me I am currently asking how many clicks can I buy for this $40 a month?