I found a bug, in the viewport, with light tracing caustics get brighter when zooming out from them or dimmer when getting closer, if I enable and disable light tracing or change the light tracing percentage it goes back to the correct brightness.
(For some reason the gif resolution gets very small)
I would try this setup in the compositor and try adjusting the sharpen and often filters before they go into the denoise node… make sure you turn off denoise in the render panel so that you can manually denoise it in the compositor as shown.
in luxrender there are different pixel filters, lancoz i think is the sharpest but for the compositor setup i showed you might want Gaussian to start of with then sharpen it so you dont get black ringing artifacts so much.
I might try with that blend file but do you have a photo for reference of the look you are trying to achieve?
I updated the scene, changed a bunch of render settings and gave it a 5 min time limit and separated the caustics into its own layer, so you can do anything with them in the compositor.
The way i have set it up i boosted the caustics, denoised them gave them a filter, denoise, bloom, color, and chromatic aberration just as an example, then mixed it back in with the color add node.
Enjoy!
Heres a render using luxrenders camera imager settings, to give Tonemapping, F-stop, shutter, ISO,chromatic aberration, vignette, DOF, bloom, Analong Film Simulation (Kodachrome 64CD)
And i gave the scene an HRDI + the glass a normal map. 18 min render on GTX1070
Also set the blender color management to RAW, and 2.2 gamma.
Use a daylight HDRI. I put thin film on the glass. i used the automatic denosie this time and no caustics boosting. These caustics come just from the HDRI no other lights rendered.