In most cases, the number of times that you plug in a SD card isn't the problem. I've never had a card that failed on me due to that and I remove them pretty often for various of my projects.

However, as with all non-volatile memory chips, they have a limited number of read/write cycles. SD cards and SSDs are both susceptible to this problem but I wouldn't worry too much in the case of SSDs. With SD cards, I doubt they are designed to function well under this kind of load. Bitcoin nodes are pretty resource intensive with the client fetching information ever so often. If they aren't one of the "better" ones, I wouldn't expect them to last a very long time. The SD card in your smartphone is probably fine since it didn't go through that many read/write cycles.

To the point on Raspberry Pi nodes, I feel that it is way more cost effective if you purchase a HDD to connect to it. It would be the best if you could salvage it from elsewhere. The sheer cost of a 128GB card is more than a 1TB WD HDD.