Sdstick - HK seem to be making in-roads to creatiing hot/warmliners at an affordable price - composite using glass and CF (see mention of the 'Geronimo' a few pages back - as this is a Siren thread, I won't go into any more detail than that).
I don't profess to know the history of the Siren, but I'd dare say a few things would have changed since the first 2004 model.
Correct me if I'm wrong, but Carbon Fibre was an elite and extremely expensive commodity back in 2004 - F1 cars would have been using it, but I'm not sure the first Sirens would have had the CF underbelly.
For what it is and the price, the Siren is one sweet flier. Love mine to death. Still makes me go sweaty when setting up for a fast, low, motor-off pass. Simply love that sound.
As an introduction to hotlining, it's a great plane. But, as you said (and I said way on back), it's more of a fast warmliner than a true hotliner. Then again, you're getting a taste for hotlining with a flying Siren for about half the price for just a basic airframe when compared to an Alex Enigma.
A Siren with a fully composite slippery airfoil would be the next evolution I'd like to see
But that would probably push the price up - and into a range where for one or two hundred $ more you'd be in genuine HOT
From what I've seen, bought, built and flown lately, I think glass/CF fuzes with balsa sheeted foam-core wings are the compromise between price and performance. As soon as you start talking moulded wings, the price seems to jump a fair bit...