I think more efficient speakers are indeed worth exploring. However, be aware that they will sound different, especially if they have horns. They will have both virtues and vices that are different from what you have now, and it may take some time to decide where the better balance is. If possible, try to find a club or group near you; in any case listen to as many varieties as you can. And, much as I appreciate the virtues of single-driver systems, very very few of them can be cranked really loud without cone-excursion-limited distortion.
It seems from your post that you need 30 watts (6dB more than 8 watts) to obtain satisfactory loudness when you want to crank it. That's not surprising; 6dB is subjectively "twice as loud" according to the psychoacoustical scholars. Two tube amps bridged or otherwise acting in tandem will only give you twice the power, i.e. +3dB. To get +6dB you'd need four amps.
My preferred method of multiplying amps is to wire the output winding in series. This raises the impedance linearly:
Two 8-watt amps using the 8 ohm tap in series gives 16 watts into an 16 ohm load.
Two 8-watt amps using the 4 ohm tap in series gives 16 watts into an 8 ohm load.
Four 8-watt amps using the 4 ohm tap in series gives 32 watts into a 16 ohm load.
Two 8-watt amps using the 1 ohm tap in series gives 16 watts into a 2 ohm load.
Four 8-watt amps using the 1 ohm tap in series gives 32 watts into a 4 ohm load.
The Paramount has taps at 4, 8, and 16 ohms but can be wired for a 1-ohms load with a slight sacrifice in copper losses. Doc B uses four of them to drive the 4-ohm midrange in the big system now in his living room. We could probably have a special run of transformers made with 1, 2, and 4 ohm taps if there were a big enough market for this approach, but it hasn't happened yet.
