The expected upward trend continues for a long time. It was a very nice investment. $ 140 is a very good value. I think that you will continue to rise during the past few days.

I thought I read some time ago that the ring signature technology is mathematically not as secure in terms of anonymity as- for instance, ZCASH or so. So is that true? I have no clue about that stuff.

Monero is getting its own version of localBitcoins. A team of monero enthusiasts based in Hong Kong have launched an alternative version of LocalBitcoins.com.
Called LocalMonero.co, the website will connect buyers and sellers of the cryptocurrency based on country of residence. Users can meet and exchange monero for cash, or buy it online from a local seller. Created in 2013, monero is a privacy-centric cryptocurrency that obscures user transactional data by use a cryptographic procedure called "ring signatures."
https://localmonero.co

That of course depends on what government you are talking about. And I would expect that anyone that has figured out how to do this on a large scale (it would have to be in BTC I would think) would not be willing to share that information without a price so your best bet would be to consult a good CPA.

...and assuming one can contact a local buyer/seller to trade with in person through LocalMonero without any strings attached, how does one go about sending/receiving a Monero transaction in such a situation without lugging around a cumbersome laptop which requires a WiFi connection?

Though I have a CLI phobia or some sort of aversion to it like so many other average Joes, I did try it on two different phones out of curiosity but could not get it to work. As you implied, it's not a viable nor a practical method of transacting on the go anyway. I guess the point is that Monero has been around a long time yet there is still no working mobile wallet app available to date. In fact, they just recently rolled out the GUI wallet.

Just because I expressed my aversion to CLI doesn't necessarily mean I don't know jack about hardware or more specifically, the difference between CPUs/SoCs of different platforms. I actually build rigs and therefore built my own little mining farm way back then before ASICs came into the scene. I also played around with RPi and have a half dozen Android devices that I also play around with. You and I probably read the same guide on the GnuRoot Debian/Monero Wallet CLI combo on Android whose links (from Reddit or Stack Exchange or both) had been posted on several occasions on this thread.

That said, you're still missing the point. Let's say that I was such a wizard of a tech geek as you are and succesfully got Wallet CLI running on one of my Android devices like you did. Is the other party that I'm gonna be transacting with in person as capable as I am in going through the intricacies of such a complex setup? There is no time to show off geek prowess when transacting on the go. One should have the ability to fire up the wallet, punch in the amount and hit send while the recipient would open up his/her mobile wallet and check to see if the transaction went through. That's an actual trading scenario in person. Same thing with making a purchase in person (primary use case) with cryptos. Punch in the amount and hit send. Showcasing geekness not necessary; in fact it's a hindrance and time-consuming in the real world. In other words, it's not viable nor it is practical/efficient.