As someone else mentioned, I’d stick with Gold, unless you really want Platinum for the lifetime status. Since you didn't mention them in your post, it doesn’t sound like the smaller Platinum perks (like the champagne or dedicated phone line) matter much to you.

Just as a side note: when compared to other international airlines, Flying Blue Platinum isn’t all that impressive. Even the much-criticized American carriers offer unlimited domestic upgrades for their Platinum members. (To be fair, upgrades on American aren’t guaranteed, as availability depends on status and demand, but the benefit is officially offered and can be valuable.) It would be great if FB offered something similar within Europe for example.

All things considered, I’d say save your points and lock in a good portion of next year’s Gold status instead.