Hey, we have similar vintages of 15" MacBook Pros, I am going through the same battle on that front, those sexy retina displays are certainly tempting and the MacBook Airs are finally getting powerful enough at the same time as the world is transitioning away from optical media. My MBP is just starting to feel it's age when I push it hard with video, music production or photo editing. (It's fan actually runs for more than 30 seconds!) I have a feeling swapping out the seldom used optical drive for an SSD and maxing out the RAM would fix that though. Then I ask myself is it worth dumping a few hundred dollars into a 5+ year old laptop when I use my iPad 90% of the time anyway?
It truly is a magical time to be mobile, the processors on the latest iPhones would put yesteryear's Mac Pro's to shame, You could have the collected works of E.M. Forster in the palm of your hand on a kindle device. I video chat with my family on the other side of the world as easily as I can make a phone call, my Sony RX100Mk2 camera fits in my hoody pocket and takes better pictures than my bulky DSLR from a few years back and as a bonus I don't feel like a complete (insert crude term for genitalia) while I am out taking pictures and therefor I find myself taking way more photos. I say make the most of the technology that is available, if you see something that would make your life better go for it! And every now and then unplug everything, head to the mountains, chop some firewood and realize that you don't really need any of it!
As for ideas, they should be constantly changing and evolving as you observe and learn. Remember, the only people 100% sure of themselves are nut-cases and fanatics!