LCD Problem -- Replace display or use MBP as desktop?

Question

Internal video is usually dead on my MBP 3,1 -- dark grey screen (but not black) with various vertical stripes. External display works fine. Internal display periodically comes back to life for no apparent reason but then fades back to its usual unhelpful state over time or if it is touched, however lightly. Per Apple, I do not have a defective nVidia card. Initally, Apple proposed their $310 fix which I've had twice before (paid by Amex)-- once for a SuperDrive another time for a logic board. Then noticing two slight dings in the case, the Apple genius said that the machine wasn't eligible for the $310 deal, as such machines had to be pristine. This notwithstanding the fact that Apple had previous logged the dings as cosmetic. At that point, the new display went up to $700 and I was told that I'd need a new logic board if I wanted a meaningful warranty. Obviously, I'm not spending $1200 on a three year old laptop. So I decided to do it myself, something the Apple genius conceded made sense.
I've replaced the data cable with no success. My next step is to replace the inverter cable, although I doubt this will do anything because the brightness controls on my dead LCD seem to work fine. That leaves me with inverter (unlikely) and the actual LCD to replace.
Do I go ahead with the LCD which runs from $150-250. If it succeeds, I may get several more months out of my Mac. If I don't, I'm looking at a new logic board which I won't buy, leaving me out $300.
I'd be tempted to suck it up and pay too much for a new Mac but I really need a 15" model with an Expresscard adapter slot -- something that no longer exists. If I buy a new laptop which would be hardship right now, it would likely be a Lenovo W510 (i7 processor, 500gb hard drive, good display for photo editing, etc.) all for $1785. My preference though is to keep this laptop going and put those funds toward a Mac desktop which I also need.
Any suggestions on the display replacement? Shall I go out and do it? What is the likelihood that I'll do it but won't succeed. Could the fault lie with the motherboard, as well?
Thanks for your suggestions.
Max
ps - Time is of the essence. I need to resolve this over the next week.

Answer 1

Thanks for the clear-headed analysis. Ordinarily, I would agree with you especially since I never actually sell old electronics. I just give them to friends and family who are behind me on the technology curve. Here's some additional information.
I've been using the MBP primarily for Photoshop but am finding with CS5 that it is slow. It's my only real computer. I have a Lenovo S10e that runs OSX but that's for fun. I have four external hard drives that use eSATA connectors (I shot 600gb of photos last year alone.) I'm starting to work with video and the MBP stutters on playback. So I've accepted that a MacPro or something like that with a high-end monitor is in my near future. I have to travel next week for an assignment with a working laptop.
I've priced the current line of MBP's and am looking at $3000 which I'd rather put toward my desktop. I can come up with the money but that will set back the desktop project and leave me with a laptop that isn't cut out for the bulk of my work. The 17" which accepts ExpressCards doesn't come in an i7 configuration and isn't very portable. If I go with a 15" model, I still need to keep my old machine around to transfer files on an as-needed basis to a Firewire hard drive.
I've seen many posts in these forums about the nVidia issue with users describing symptoms similar to my own. The solutions have included replacing the data cable, inverter cable, inverter, display and (less often and usually at Apple's expense) the motherboard. Assuming that I can live with the consequences that something else will inevitably break, the question I'd like to find an answer to is whether based upon:
the display occasionally functioning perfectly;
(ii) the external display working perfectly; and
(iii) the graphics card passing Apple's diagnostic test
I can assume that the motherboard is ok - for the moment. (I realize that every time I reopen the case to change wires, disassemble the display, etc. I'm increasing the likelihood that one day the motherboard won't be ok.)
Any thoughts?
Thanks again for your help.
Max