Self tune systems sound like the way to go, but what type of driving and RPM range are you looking at? Looking for more HP?
Upgrading costs will buy a lot of fuel - even with increased costs in the UK. Might be better off and have the carb professionally tuned. $4000 buys 1000 gallons of gas (@ $4/gal) and if you get 10 miles/gal, thats a 10,000 mile break even!
I have TWM system with an Accel DFI Gen 7 (2004) management system on my SBF 427. Part of your decision should be "if you have a problem, who can tune it for you?" Believe it or not, living in the San Francisco Bay Area, it has been hard to find someone that can tune a Accel DFI system. Seems that most people are installing the FAST system. Now I have to upgrade my firmware ($249) and add a dual wideband set up ($899), plus - probably tune up costs. Good to have a stable idle, and not worry about fuel sloshing with EFI.
Also consider the cost of re-doing the fuel system/fuel tank - if you plan to do things right ... could cost $500 - $1000.
Have you considered Webers? ... Although I have always heard that carbs out perform Webers at top end, carbs don't have that cool factor. My other toy has a 347 with Victor Jr. and Holley, but considering Webers through Jim Inglese. His system is more expensive than other packaged systems, but he will custom build your system with "close jetting", out of the box. With all of the problems I've had with tuning, electric fuel pump and now upgrading , will keep the next one simple (no electronics or computer) and cool factor for half the cost of TWM.
I actually spoke to Jim Inglese a while ago, very knowledgable, and good guy.
http://www.jiminglese.com/index.html
good luck, just my $0.02.