They were reused and were extremely efficient with a much higher unit cost than the equivalent energia stack main engine. The Soviets intended to design a carrier shuttle with reusable engines just like the US Shuttle but abandoned the effort due to reliability concerns.
That is the whole point of the space shuttle design in any case. If you can't reuse very powerful main engines that can be made to be very efficient there is no point in using a shuttle-truck design in the first place.
> while the Energia from the Energia/Buran combo would have been useful in its own right (sadly the Energia was discontinued with the Buran).
The energia was suboptimal for launching very large items due to its requirement that payloads have to carried on the side. This increases the weight due to atmospheric shielding that cannot be jettisoned and, more importantly, means a third stage cannot be used for efficiency. Every payload also has to be able to deploy itself into the correct orbit which requires custom development for each launch payload. So while energia was powerful it was very expensive as a standalone launch platform and never would have seen much use and consequently was never seriously considered as a future development platform.
The soviets would have done better just to develop a lh2/lox successor to the failed n1 rocket in the first place; especially if they didn't think the shuttle was going to be economical. Instead, they developed a sub-optimal launch vehicle that was itself based on a flawed concept and they had every intention of running the program out to the year 2000 even with a handful of launches scheduled and development costs that were already higher than the US shuttle.