Might want to start looking into older Nintendo games if you really want to hit plat this year. My advice would be to check for cheaper used / older games. Even if a copy is used I would bet 90% of the people that bought them never bothered to register their games.
Remember you have a decent amount of Wii and quite a few DS games that give coins. If you just hit gold status that means you are some where around 300 coins out of 600 needed for plat. I would venture a guess that 3ds is worth at least 200 coins (hopefully they give coins for it).Don't forget about post play surveys too (I have about 100 coins worth bulit up for a good head start for next year). You might want to just grab at least one nintendo 3ds game even if they don't look great (I am grabbing pilotwings for example since I need something to play on it and Street fighter 4 is not going to keep me occupied for 2 months before the big titles come out for it. A 3ds game should be worth about 60 coins for a 40 dollar game (10 coins extra for buying early and 10 coins later for post play).
In regards to just "buying games for coins" the nintendo plat reward has been great each year so far while the gold reward has been very average so I would say it is worth it. Also, a lot of old Nintendo games are not that bad: I think Dragon Quest series (about 4 of them on DS now I think) all can be registered with Nintendo.
