Best Mac/iPad set up for students

Hi, basically I want to get some advice on what would be the ideal set up for me as a student. To start I'll let you know what my current situation is and why I need the advice.

I have an old, and slowly dying MacBook Pro that I've used for years as my main computer. However when I started uni, (I guess for most people on The Verge this will be college), I wanted something more portable so I bought a MacBook Air 11 inch, the 2011 i5 model. My MacBook Pro sits on my desk as a glorified desktop as the battery doesn't last more than half an hour and I take the Air to lectures. I also have an iPad which I use mainly for non-work stuff particularly browsing as the MacBook Pro has been getting increasingly frustrating to do anything on of late. I can't stand the problems with it any longer but can't decide what to do. My current thoughts have led me to these options:

1) Buy an iMac and keep the Air and iPad just for mobile.

2) Hook the Air up to a monitor when I get home and then take it with me to lectures. (Worried whether this will be powerful enough as I am an economics student and have to use large spreadsheets and other larger software packages).

3) Wait to see if the rumours are true about a cross between the Air and Pro ranges, buy a 15" MacBook Air if this comes to fruition; sacrificing portability with perhaps the iPad stepping up as more than a play thing, but hopefully gaining more power from the laptop. In this case I would sell my current Air and still probably get an external monitor as I do miss not having anything larger than 15" to watch movies on as well as just general computing.

4) Go another route which maybe someone could suggest.

A further caveat is that I do want a larger screen as I don't have a TV to save money and space so I need some solution with a larger screen size.

Any help would be greatly appreciated.