Will I be wasting my vote?
Principles cannot be compromised - only abandoned.
The simple answer is that you are never wasting your vote as long as you are voting on the principles you believe in. Principled ideas are based on knowledge and understanding of the purpose of government. If you are not voting for those ideals then the message that you are sending with your vote is that you do not want the politicians to uphold your principles. The only way to put good ideas into politics is to use your vote to show you are behind them.
The complicated answer is still no, but many people 'play politics' with their vote and choose 'the lesser of two evils'. This is a fallacy that some voters use because they do not want to 'lose'. If you are a principled voter then the only way you can lose is by not voting for those principles that you hold. If you believe one option is leading down a bad path, but another option is moving down a bad path but slightly slower then you are still going down the same path. Principled voters choose the best option even if they might 'lose' a single election because that is the only way to really fix the problem. If you want to make the best choice that means you have to stop making the wrong choices completely. The ideology and principle of your vote and voice is only heard when it is used, and silenced when it is compromised in hollow attempts of victory.