Tefilla Question of the Year

My seven year old son asked the following question tonight, right before bedtime:

I know that there is a 'song of the day' for each of the days of the week in our siddur, but why isn't there different davening for each day - why do we daven the same thing each day? 

Good questions - any good answers out there?

Pslams by the Sea

I came across the following question answered by Rabbi Yaakov Cohen of the Beit El Yeshiva:

Question: Can I say Tehilim on the sea side without a shirt on?

Answer:  One should dress respectably when praying or saying Tehilim. But there is no Isur (prohibition).

I love this particular question and the response - which is totally appropriate and subjective. The questioner is comfortable enough to daven at a beach or felt moved to pray after bathing topless.  The rabbi recognizes that there is a need to promote proper decorum in prayer but that there is no real restriction to spontaneously say psalms.  

Think about it - who wouldn't be at a beach, pondering the eternity of the tide and not think to praise Gd and nature's amazing cycle?  Just to bridge to a post last week on davening on airplane - I am not sure I would recommend gathering a minyan of people to pray as it might bother the other sun worshipers.