Wash & Lube?

On average I tend to get better groups after washing and lubing. But not always...I recommend testing before and after so you can find the best possible results. And don't expect it to track reliably over time because it will vary from tin to tin (different batches / mfg dates)...for example if you find your tin of 34gr JSBs group better after washing and lubing, the next time you buy them they may group better straight from the tin.

The side benefit of helping to extend the time between cleanings is nice but I won't trade accuracy for it. Not even a little.

My preferred approach is to dump them into a wire strainer and then spritz them with Purple Power degreaser, and tumble and swish them in the strainer. Then rinse and spread them out on a towel to dry. Or sometimes I'll put them in the toaster oven at 200F to speed it along. Then back into a tin with 10 - 12 drops of White Lightning bicycle chain lube (the wax version, not the silicone). Tumble in the tin until it's evenly distributed.

For pellets that have loose flashing and pronounced parting lines, the tumbling tends to help remove it. It helps with Crosman pellets in particular:

https://www.gatewaytoairguns.org/GTA/index.php?topic=134454




 
I wash mine in acetone, then into a strainer and swish strainer of pellets in the acetone, then pour the dish of acetone back over the pellets into another dish, I use 2 glass dishes and there is always a lot of lead dust in the clear dishes from pouring over the strainer! Then onto a towel to air dry, followed by 4-5 drops of fp10 in a empty pellet tin and add pellets and rotate and roll to distribute the lube 
 
Has anyone tried lubricating their pellets with a silicone spray? Any drawbacks from it?

I wash my pellets, but haven't tried lubing them yet. I have wax bicycle chain lube and 100% silicone spray.

The silicone won't leave an oily residue in the barrel that can attract and hold dirt or dust, that is why I ask.

Yep. Most use silicone (myself included), although I have some barrel and projectile combos that shoot noticeably better with Slick 50.