Hard to say really.
A $200 purchase in 2000 requires $280 today.
A CLE-LAX ticket on CO in 2000 cost about $200. Today that ticket on UA is $400.
A CLE-LAX ticket on CO in 2000 cost 25K miles. Today that ticket on UA is 25K miles.
Not sure what $200 purchase turned into 10x Yechi.
Back in the 90s 30,000 PanAm miles took us RT HNL-TLV via JFK (and we rearranged the flight coupons).
Let's not talk about the ignorance of agents that I took advantage of when DL took over PanAm, to allow me RT in J from PSP to TLV for the same 30,000 miles.
When I started accumulating miles on BA, I actually managed to get some good use out of the program for NYC-TLV-NYC tickets (including pleading with them to open up availability for my mother to come to me for Pesach after my father had passed away). Now the YQ on BA tickets is more than what I pay to fly kids RT revenue JFK-TLV.
I've never been big on UA, but I've witnessed at least one official devaluation, and the unofficial devaluation with the virtual elimination of saver award space into and out of TLV, as well as the elimination of the ability to piece together itineraries not found as a direct point-to-point online search.
I bought my sister a OW ticket from Australia to TLV in J for 40,000 AAdvantage miles. IINM that's 80,000 now.
And while CLE might have had it's reasons for revenue tickets going up, we're flying from NYC to TLV for the cheapest fares I've seen, both in economy and in business, and I'm booked to go to FLL this week for $69 RT courtesy of JetBlue vacations (thanks Dan for spelling out the steps on DDMS).
I don't think you can argue that miles haven't been devalued, and are subject to further devaluation at a whim. And while the USD could devalue, as it is pure fiat currency, it is not likely to happen rapidly, it is after all, the world's reserve currency.