Any advice/thoughts are welcome. Thanks.
your message confused me because you didn't really state which models you were looking at. I can offer this advice, macs tend to hold their usefulness for years. i can
still use my 12" PowerBook for general tasks and that unit is a decade old. no, it won't play crysis, but it will surf the web, do word processing and the like. so no matter what model you get you will easily get 3-4 years out of it. even your existing unit is 5 years old and if it weren't dying you'd probably be just fine with it.
anyway. my advice, go for as much as you can afford. prioritizing RAM and storage space over CPU. upgrading RAM on these units is not possible, so get more than you think. some 3rd party vendors come out with SSD upgrades (OWC being one of them) so it might be something you can do down the line. while having more CPU power is nice, the bang-for-your-buck just isn't there. $200 for 200Mhz? that's going to get you what? a web page rendered .5 seconds faster? benchmarks are nice numbers for people to brag about, but consider
your real world usage. if you're not folding proteins then do you really need the Ghz?
these new haswell designs will probably last apple a good 3-4 years before they move on, even then you'll be be able to use the laptop long past that.
if plugging in external drives is a pain consider a network solution (assuming you have wireless at home) and get a NAS unit like a Synology or Drobo. no reason to store all your photos, music or videos on your mac itself, offload them to a raided unit for extra security and save space on your laptop. or go with dropbox or the like if you want to store it "in the cloud."
good luck!