Unless your doing something very illegal and you want to make sure you don't get caught, you should use opaque blockchain, ...as a payment tunnel.
I think you completely omit the crucial importance of ownership privacy. With out it, your loved ones are in constant danger of kidnapping, powerful and ruthless people can target you for milking, and you are disadvantaged in every negotiation.
At any-rate Monero is doing the best job of all the crypto-note coins
It's always nice to find points of agreement.
Question1:
How high a probability do you think it has that will happen again ?
That is an excellent question, albeit complex to model. I shall try to develop a model for this, since it is, I think, a very useful technique to develop. The most closely analogous defect in Bitcoin was a singular event. That analogy can be used as a prior.
Question2:
How much of your investment portfolio should be invested in this type of (even more risky) crypto investment in comparison to other crypto currency's?
I claim XMR is much less risky than Bitcoin. Bitcoin governance and political risk is many times higher.
I urge people to hold at least 10% of their assets in diversified high quality crypto, primarily xmr and btc, in that order. The upside potential of XMR is more than 60x the upside potential of BTC. But for high net worth individuals I think the value of the opaque chain is much higher, as a store of value, modulo the volatility issue. In the long run, wealthy people should hold a majority of their liquidity in Monero. A provably correct implementation would facilitate that.