I can only give you my personal experience, it can be a heated topic.
1) Tube is better
2) The tube sound, to me, mostly occurs in the high-power amplifier section.
That is a tube Pre will add a small bit of warmth, but a tube Pre and Power Amp is where my sweet spot is.
The aural hologram is from the small 3rd order THD and slight compression that the power amp delivers, from what I've tested.
Pres provide these, but usually in much lower doses.
Your mileage can vary and use your own ears!
Get to a good high-end shop and put in a few hours to see if the investment would be worth the difference in sound.
As a side-note, the ST-140 is about as "tubey" a solid-state amp as I've heard.
If you sell it, LMK, I'm thinking about upgrading the Rotel patio amp and tubes aren't an option there.
Lastly, implementation is not to be overlooked.
A poorly designed tube amp will not be better that a well-designed solid state one.