A quick thought on how multiple attacks might work without dramatically increasing damage when you acquire an additional attack. Let's assume that they also move towards weapon dice affecting your damage output, rather than having martial damage dice explicitly. So, at first level you get 1[W], and that might increase every few levels until it reaches some maximum. Along side this, independently, you might have a maximum number of attacks, starting at 1 (+1 with two weapon fighting) and also increasing every few levels until it reaches some maximum.
If we take an imaginary mid-level character who has a maximum of 2 attacks per action and 4[W] damage. There are several ways you could dictate how multiple attacks work, but I will discount that each attack does your 4[W] damage, since that does provide the dramatic increase in output mentioned above. You could declare before each attack how many [W] you are committing to that attack, roll and deal damage if you hit - I think this would be a little slow though as people have to assess likelihood to hit, toughness of target and so on each time they want to attack. You could declare *after* each attack how many [W] you are committing to that attack, roll and then choose how much damage you will deal - this still requires you to think about toughness of target, but less about your chance to hit. Now, that might be a bit too generous - you miss once, but there's no penalty other than you must commit all your damage to your remaining attack, which is no great loss against a single target. So, a small penalty might be that you lose 1[W] damage for each attack you miss. Multiple targets? You have the flexibility to attack different enemies, and you can divide the damage up on the fly. Single target? You're encouraged to commit all your damage if you hit first time, but if you *don't* then you get another chance.
I think a simple system like this would make martial-oriented classes have much more impact in combat. Not only will they be able to slice up multiple enemies with a single action, but they are *very* good against single targets, as their damage is made less all-or-nothing. The progression in damage output would also be smoother - no sudden doubling, with the most dramatic increase appearing when you get your second attack - though this would be an average increase, the maximum would not change.