CyberSyn - freeware for newbies;
CyberSEO Suite - commercial for professionals.
Both are incomparable with FWP but they work faster, support big range of non-standard RSS (in case of CyberSEO Suite RSS
and XML) feeds and they have flexible scheduling possibilities.
As about your last question. Yes, you will need to re-syndicate your existing posts (both CyberSyn and CyberSEO Suite are compatible with each other but incompatible with FWP). However, if you choose CyberSEO Suite you will be able to re-syndicate all 1500 posts with one click, because it's the only plugin which allows to syndicate ALL posts from the another blog including those that are gone from the feed years ago.
For example, let's look at
http://www.rbblog.com/ - this is a sponsor hosted blog which contains 2,331 posts (since 2005), but there are only 5 posts in feed:
http://www.rbblog.com/feed/, thus all the existing plugins (including FWP, Autoblogged, Wp-o-Matic, CyberSyn and others) will aggregate only these 5 last posts. But not the CyberSEO Suite.
It will aggregate all 2,331 posts right into your blog! The only thing you need to do for that - simple enable the "Parse WordPress archives" option in the feed settings menu.
