How much difference does a phono stage make?

From an NAD PP2 to an ARC PH3?!...I think you'll notice a huge difference. I had an Acurus P10 with my ACE HO which I thought was really good if not awesome, until I traded it in with my current Conrad Johnson EV-1... I was and I'm still blown away by the difference. BTW, not that it should mean anything but, Michael Fremer of Stereophile gave the C-J EV-1 a class A rating while the ARC PH-3 -I believe got class B. And BTW again, if you haven't already, I still think you should research the Primare R20 -it's in you're budget -new!

PLENTY! Go for it and you will be amazed. IMHO, the difference can be more obvious than any other change in a system. Cheers.

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.