I'd have to disagree there.  Killing creeps late requires a good strategy otherwise the creeps would just run straight through the level and you would lose.  I think the scoring system works well as it was mostly what had me back playing the same levels over and over trying to beat my highscore.  The late multipliers make it more challenging to get a higher score and push you to take more of a risk which I found made the game a lot more enjoyable.

I can see the merit of the risk vs reward system, but when it really comes down to it, it really only rewards stacking as many possible towers at the last second as possible. A lot of the criticism I've seen regarding strategy in GD is that with the update to the shock towers, stacked defense simply becomes a matter of jamming laser towers and shock towers into the end zone. Indeed, it's the only reliable way I can find to increase my high scores, simply by moving the towers a few pixels at a time toward the end zone each time I play a map again, until I'm finally "too" far, at which point random chance is as big a factor as anything else. My thoughts on a more complex scoring system came mostly from having played Defense Grid on the PC. The game itself has more complex rules for scoring, some of which is actually based on your resource management, your lives remaining, and your general performance in the map. I find that it generates a much more widely spread top players board, as people experiment and try new tactics.

For the resource management, it actually works like interest in a bank account. Starting at a certain stage and above, you gain interest on your available resources; the more you have banked, the greater your interest payout is with each 'tick' of the clock, which is every few seconds. In addition, for each tick that you go without spending ANY money, the interest percentage itself increases very slightly, and resets once you finally spend money. That particular trade-off grants its own unique risk vs reward scenario, but can be dynamic to each player's individual play style, much more so than just cramming towers in around Point X or Point Y. Different strategies allow different rates of upgrade, versus just adding one more shock tower every few waves. Players also get partial credit for the resources spent on the towers they buy, as well. There's risk/reward calculation in that system, in that you can actually get more money by buying lots of small towers and not upgrading them, than you can by building a few key towers and powering them up strongly. The lower amount spent is actually banked, and presumably gains interest, raising the resource calculation into the score at the end.

Scoring based on lives works as a direct multiplier. After all other calculations, the total score is multiplied by the number of remaining lives, resulting in your final score. This directly impacts bad performance, whereas as far as I can tell in GD, lives only matter so long as you still have one at the end of the map. The only real tradeoff for lives is that you miss the chance for a +50 multiplier, plain and simple. Then again, that tradeoff only matters if you're end-camping.

It's mostly just food for thought. I just found it odd that the better you actually do, the worse you score, unless you play by the sole concept of camping the end point as closely as possible. At that point, it's less about strategy than it is about overloading the nearby space as much as possible. I prefer scoring systems which take ALL types of gameplay into account, and reward good performance versus bad, not just smart and risky versus everything else.