#1
If i buy a squire stratocaster and upgrade the strings/pickups/bridge/nut then could I get a decent tone out of it or no?

Or should I build my own stratocaster from kits/parts?
#2
The affinity would work nicely. Anything else will probably be the same as any **** strat, unless you go all HQ parts.
Gear
Fender Thinline Telecaster Deluxe

1983 Aria Pro II XX Deluxe Flying V

2007 S101 EGU34

1963 Kay Vanguard

1964 Kay Vanguard

AXL Badwater SRO

Hondo Strat

1974 Acoustic(brand) 134 4x10 combo

Epiphone Valve Jr.
#3
so if i do upgrade it and spend 300-400 on a 100 squire would i be able to get it to sound better than the american counter parts?
#4
No. More like $179. Alder body = more potential win. Then do what you will to make it awesome.

http://guitars.musiciansfriend.com/product/Squier-Affinity-Series-Stratocaster-Electric-Guitar?sku=510423
Gear
Fender Thinline Telecaster Deluxe

1983 Aria Pro II XX Deluxe Flying V

2007 S101 EGU34

1963 Kay Vanguard

1964 Kay Vanguard

AXL Badwater SRO

Hondo Strat

1974 Acoustic(brand) 134 4x10 combo

Epiphone Valve Jr.
#5
...but if you're going to spend 4-5 hundred you may as well get a good strat to begin with. It'll be a lot better than a modded Squier in the long run. For that kind of cash you can find a used Classic/Classic Player's Series Mexican. Maybe one of the discontinued Strat Specials or even a Tex Mex or good Standard. All great guitars and lightyears ahead of any Squier.
#6
I modded a Squier, and it's now the best Strat I've ever played, mainly because it's exactly what I wanted. V profile neck, wilkinson bridge, Sperzel locking tuners, new pickups, electrics, etc, etc.

Would I do the same again? No.

If you look at how much I've spent, including the guitar to strat with, I could have probably bought an MIA strat (when the £ was high against the euro/$ and before the recent price rises).

I don't regret doing it, and I play my heavily modded Squier as much as I play my MIA Tele (and it plays just as good), but I'd not have set off down that road if I'd know where it would lead and how much it would have cost over all - The only things that are left stock now are the body (which is Alder) and the neck plate.