Most tours allow visitors just 1 night at Machu Picchu. What do you think about spending a second night there?
Have you been there? In hindsight, would you have schedule more time at the site?

Here is my Peru itinerary:

3 nights Lima
2 nights Sacred Valley
1 or 2 nights M.P.
4 nights Cusco
1 night Lima

Any comments or ideas would be welcome and appreciated.

I would spend only one night in AC. The ruins can be seen in a day. However, it is best to see them when the crowds of daytrippers from Cusco are gone (they arrive around 10am and leave around 3pm).

Note you may want to reduce your time in Lima and Cusco and increase your time in the Sacred Valley. Ollantaytambo has more charm and character than either city.

Agree with RBCal in terms of cutting time in Lima and adding it to your time in the Scared Valley esp Ollantaytambo. We liked Cusco and did spend 4 nights there. We found plenty to do and see in the Cusco area during the day. We didn't spend the night at MP (or in AC). We took the train from Ollantaytambo arriving around 8:30 am and leaving late in the afternoon. In retrospect I would have liked to have had 1 night and perhaps even 2 in the area. While you can see the ruins in 1 day, spending additional time there just to sit and soak it all in would have been fine by me. We were there in April and it got busy for about 2 hours between 11 am and 1 pm. After 1 it was really empty. Enjoy your trip!

Another option, depending on what you want to see is to go to Nazca from Lima for a couple fo days to see the lines from the sky. Ive been to Machu Picchu 3 times with groups and have stayed one night every time, only time regretted one night only was when it rained all day ! But depending on time of year you go that shouldnt be a problem. Just stay there till late pm after tour groups have gone or get there early next am before groups arrive. You'll pay US$36 for each ticket each day and US$12 for the bus there and back each day each person.
Have fun, any more help needed just ask.

Nazca can easily be done as a day trip from Lima. No need to spend the night. If you search Nazca, I've posted in great detail about it.

We stayed in MP for 2 nights, and I think that I night would be sufficient.

Also, we saw Nazca lines on a day trip.