I agree with most of what Torquelink said.
33 seats (yeah you can fit as much as 36 into SF340 but this is much hardcore than 189 in 738) market is balancing on the edge of break-even. Basically to make a sort of low profit on SF340 you have to charge pax EUR 100 per hour flown at somewhat reasonably good load factor. And we talking about aircraft with market lease rate ranging from 20 to 30k USD. If you have a new machine at USD 12m cost, lease rate would be in 100-150k area and there is no way you can justify it with 33 seater at the current market except a very few niche routes.