According to the docs, the -filter parameter qualifies the path parameter so I don’t think you can filter it that way. You can pipe to where-object to accomplish what you are trying to do.
I use (Do-Something).Property in similar cases which seems to speed response times, but I’ve yet to measure it against Where-Object. Below, I put the new files count inside a dictionary object in case each item needs to be called separately (may still be called in whole); the key MyServer would be replaced by the name of current server instance.