I would suggest that you try a few alert tones to see if any of them give you better performance. Volume dynamics vary from alert to alert. By going into the click app and tapping Alarm > Edit and selecting any alarm you will see the settings that you can change. One of the settings you can change for a given alarm is Sound. Tap this option to select the tone you would like to use.
One tone you might find more to your liking is the one titled "Alarm" — this tone is much more "explosive" than the standard "Marimba tone.
You could also try recording your own tones in GarageBand. GarageBand has a project type for iPhone Ringtones. When you create your own ringtone you have much more control over the specifics of the ringtone and can even do things to increase the gain on the tone itself.
Of course none of these tips will do anything to increase the actual power of the built in speakers (which are necessarily small). One thing you could do to help in that regard is to think carefully about where you place your phone. Placing your phone in a glass cup at night (while a bit dangerous in the morning when you go groping for it) can increase the volume significantly.
Hope that helps.