What many people forget is that with image editing that which you interact with most is the monitor. Hence investing in an appropriate panel and learning how to use it can make a huge difference in the quality of final rendered images.
Not knowing what your current computer contains you might do just as well cloning your hard drive to an SSD and bumping the RAM up to 8gb. I know for a fact that Photoshop CS4 will run on my lowly ancient Core 2 duo laptop (when I used it for such but it has been a few years) and process 16megapixel images at 16 bit depths without choking so I am not sure what you see as your current issues.
If you do unattended CPU intensive chores like video rendering you can perceive the increased efficiency of more modern CPUs. Light Room can have speed issues no matter what platform on which it is running.
Whatever you get put an SSD in the thing. The difference an SSD makes in boot and disk access times is the most perceptible speed bump to the way normal humans interact with computers.
While tests clearly show differences in the efficiency of Intel processors going from Sandy Bridge (2011) to current models that does not translate into what users perceive when using most image editing programs because the speed at which humans process and interact with computer information is infinitely slower than what a bar graph of CPU throughput can demonstrate. That translates into people feeling their computers are "fast enough" and has slowed the mass market computer upgrade cycle.
I have shotcut Installed on a 128gb USB thump drive. It appears to run fine on both my home desktop and my work laptop. I keep all the files I need on the thumb drive. Not by design it’s fairly portable although you could wear out the flashdrive and lose your data depending on the quality of the drive(something I haven’t seen happen on most recent drives but is always possible since flash drives don’t wear level or have the endurance of ssd’s) beyond suggesting a SSD over a flash drive I wouldnt worry too much.
Could this kind of mobility cause me trouble in the future?