How much difference does a phono stage make?

For analog Playback the Phonostage is THE Key component. No other unit can win or decrease the signal more.
Based on that, I always spent the most money for that. Even when going back to
my beginning when I started, I had a top Phonostage even with cheap turntables
(for example, even when using a RB 300 and a 250$ cartridge, I had a Phonostage from Jeff Rowland)
Most do the other way, expensive Analog rigs with inferior and overpriced Phonostages....

The phono stage is the weak link in most analogue chains. Get the best you can stretch to afford.

Agree with all the above.

I've owned $150 cartridges and $5,000 cartridges. I also own an $1,800 preamp and a $12,000 one. Like Syntax, if I had to pair the lesser of one with the greater of the other - and could only keep one combo - I'd keep the good preamp + a cheap cartridge, not the cheap preamp + a good cartridge.

The same is true of turntables and tonearms vs. cartridges. If I had to choose between my $1K rig + a $5K cartridge or my $11K rig + a $150 cartridge, I'd choose the latter every time. $150 cartridges play better than you'd think possible on a good rig. $5K cartridges on a cheap rig just reveal its flaws and shortcomings.

In general, the expenditure or upgrade order should be:
1. phono stage
2. turntable
3. tonearm
4. cartridge

In your case, your next upgrade after the phono stage should be speed control for the Scout, which will also make a nice improvement.

The PH-3 is a very good phono preamp. It is an older model(not the lowest end model) It was at one point ARC's top of the line model.(model years 1995-1998) You will notice a significant difference in performance from what you have now!
For those who don't know, the line of progression of ARC phono preamps: PH-1 and the Reference models: Reference 1
PH-2 Reference model 2
PH-3
PH-3Se
PH-5
PH-7

Totally agree w all posters above.