Are there any websites like the Taxonomic Name Resolution Service, but for other plant attributes?

I’m not sure I understand what you’re trying to do… do you want to enter plant names to find out what attributes they commonly share? I think it’s unlikely you will find that, since most of these attributes are known in ranges instead of single values.

Put another way, your question might be about finding a botanical key to plants (i.e. something you would use to narrow down a list of species that share traits as you give more and more specific descriptions). Mostly, these are not global, but organized regionally (New England, or the Rocky Mountains, or the UK, for example). So it might help for you to look for keys to your region of study.