I know a couple breast cancer patients that had theirs over 10 years. One was NED for over 5 years and then had to use it again. The main "shelf life" for ports is in correlation to the number of "sticks" it gets. The self-healing material that closes after being poked does have limitations to how many times. But if you aren't in active treatment, you will never come close to hitting that mark. If it is in and not giving you any problems, and you have such awful trouble with veins, it makes sense to keep it. If you don't and even have other medical problems, it might mean a PICC line needs to be placed for you - so if you keep the port you can avoid that.
I agree with the aspirin each day if your doctor clears that (with your other health issues). The biggest risk a port causes is that of blood clots, so the aspirin can help guard against that. Just make sure to get it flushed every 4-6 weeks if you want to keep it in. No point in keeping it if you let it get clogged so that it won't work anymore.
If I didn't have such awful luck with ports, I would have had one for 3 1/2 year at this point, but instead I am on #4. I had no choice with #1 coming out due to infection on insertion (and a hospital stay with that). I was wanting everything to do with cancer and chemo out of my life and out of my body after my first 12 tx of chemo - believing I was cured, so I chose to have #2 removed (which landed me in the hospital with an infection again). I swore #3 was my last port for life (especially since my lung was punctured on insertion), but then it got a hole in the catheter and the plastic was dangling, blocking my subclavien and causing problems there, and anything going in was just being pushed into my chest cavity, not the vein. It isn't a problem to place a second port should you need one later, but if you get to the multiple port point, it can be an issue. The first attempt to place #4 for me didn't work - I had to go back again... (the subclavien was so damaged on the left that they couldn't use that side and I was getting radiation on the right side, so they couldn't go there - after radiation was done they did the right side, but had to move farther out towards my armpit to get away from scarring areas of previous ports)
If you have problems with it, you will know. It felt "off" with a weird popping sensation when they tried to flush it, and 4 weeks later it was worse. By the next time it really hurt and wouldn't work, so I went to the cath lab where they found the problem with the last one. If you get a blood clot, you'll have pain in your chest, and possibly radiating over the shoulder and into the back, or down the arm. just pay attention to anything feeling odd when you get flushed, or pain in your chest, neck or shoulders. It isn't likely you'll have any problems, but if you know what to look for, you'll be prepared if you do.