My view is that if you fly mostly Finnair, and not that frequently to push it to the limit, and need only the "basics" = fast-track and lounge, then Silver is absolutely enough. Not even Gold is worth extra effort.
But then, I agree that going further, Platinum is not really a big extra on top of Gold UNLESS you really extract the benefits of it such as First Class lounge at some airports and the numerous "inofficial soft-perks" that Plats get. If those are beyond of your use/avail, then Gold is equal IMO.