don't buy any alt-coins ... just mine them and sell for btc or ltc. maybe at most buy some LTC because i think they are undervalued at this time best strategy i've found so far is :
look for new coin launch mine as soon as it launches wait for it to get tradable at an exchange sell within first day or at first sign of price going down
sometimes you will get stuck with coins that never get to a market (exchange) which means you wasted your time
if you want to avoid this strategy, another reasonable option is multipool mining. thats a pool that switches to the most profitable coin of that moment. you will get lots of different coins this way though, be ready to do some work shipping them to exchanges and selling them (for btc or ltc)
I have no idea what the yen is at, but the BTC has been doing pretty good the last few days. Today ZYNGA started testing with accepting BTC payments for some of their games (farmville and such) .. I think this will give another boost, or did already. Either way it's good news. We can use more good news since the bad news past few weeks has been relentless on the price of BTC !! imho BTC will go past the previous record of 1200 pretty soon .. but let's wait and see (and dont take investment advise from me .. im such a noob)