How old is your laptop? Are there any expansion slots available?
Of course you could upgrade the internal storage, that should be the best thing to do performance-wise. But im not sure if thats really needed in your case.
Some laptops allow quite easy access to your hdd, you should check out the back of the device. Otherwise its some more unscrewing and stuff.
Its even possible to "clone" your existing system, keeping all the data, while expanding the size of your main drive along the way. That would require another computer and some software tho.
- "Was planning to use it primarily as a media dump with minimal writes done. Still a bad idea?"
Well, theres better alternatives. You were initially talking about a simple sd-card, so i guess you dont really need that much extra storage anyway, right?
I can understand that you dont want to have an external hdd plugged in all the time. But how about a mixed solution?
As it's generally a good idea to have a backup of your data, you could simply get yourself a good usb stick (a "nano" version maybe?) , these arent that pricy anymore and you can get quite a lot of extra space without spending much money. In addition, and generally, i would recommend making a backup somewhere else from time to time.
For that use, you could plug in an external drive from time to time and copy everything over, depending on how important that data is.