Once you go through something more than once or play it for a long time, a series or game in general (Pokemon or anything else) will eventually get boring. All Pokemon games will get boring wether you've played through once, twice, one hundred times, etc.
I picked up Platinum like 2 weeks ago and a DS and I'm on it everyday when I can be and I find the excitement after taking a relatively long break because I didn't buy a DS when the new versions and 4th gen. games came out. I've already even restarted my file midway because I didn't like my team or how I approached by raising them so I started over after beating Wake and now I'm at Wake again with a 4-Poke team that I love so far :)
I'm sure by when March roles around I could possibly be tired of it but it all depends on how you approach Pokemon and how you play through each time, the team you use, what you're playing for (training, shinies, beat game, etc.) and any other reason.
I love the series, you just have to find your own methods to stay occupied. FYI, Wi-Fi or online play for any system or game is SO MUCH MORE FUN!