If you are using memory intensive systems, in memory data bases, video editing, high end graphics or many active tasks, then yes, it may help. If the bulk of your work involves heavy I/O, then a SSD may be more cost effective.
It's very much a law of diminishing returns on memory, if you don't have enough for the work you are doing, then it's the best investment you can make. But once you have enough, the return on the excess isn't great.
It's all about balance, try to establish which part of your system is most stressed and address that first. Memory is one of the more difficult components to measure (unless you don't have enough) but more than enough will just result in no longer needed data cluttering up the system "just in case you need it again".
I.m not sure the speed increase you mention will be too significant, it's still way slower than your processor - that's what your caches are for but if you are replacing the existing memory, you might as well go for the best your machine supports.
A bit of analysis with your resource monitor may help.