Hi there, firstly thank you very much for your detailed feedback! We love hearing and learning from our customers' experiences.
With regards to Feed to Post and feed sources sometimes showing errors or slowing down, it's important to understand that the errors are most commonly displayed when there is an issue with the feed source itself (such as the site being unavailable), so these are not issues that WP RSS Aggregator can solve.
As for the staggering of updates, this is the ideal way of ensuring that there isn't too high a load being placed on your server which could cause the import process to get stuck at some point or another. Having the imports staggered a few minutes or hours apart should not affect your readers and it will help very much in maintaining a steady flow of posts being imported.
Moving on to Full Text, had you contacted our support team about this? We do our best to solve such issues with the full text script developers, however sometimes adverts and such are imported since they will be a part of the content. That's why we have the Extraction Rules feature to exclude them from the imported content. If you need any help with your extraction rules feel free to open a premium support ticket :)
On to Keyword Filtering, I understand that in a case such as yours it would be a paid to add so many keywords in the filtering options. Although the majority of users won't have this problem, we would still consider including such a feature in the future so please do submit a feature request with some more details and I'll have our developers look into it.
I hope this has covered all of your issues, and please do feel free to contact our support team if you haven't already so we can help you figure out these issues.
As a sidenote, please be aware that this forum is meant to review the free version of our plugin rather than the premium add-ons, however we still take all criticism and suggestions on board, so thank you again! :)