cshuang: Depends on how much you're willing to tinker with it, wait time, and how much money you're willing to part without crying inside.
For a non-fussy experience and the ability to pull a shot + froth at the same time, pick the Oscar. (And yes, that's a sweet deal). The Silvia and Classic is a single boiler, and you have to wait a little between tasks. Not a huge wait, but ya know the new generation... *waves tongkat*
Silvia vs Classic - Between the Silvia and Classic, the additional 1k for the Silvia seems to be mostly for a bigger boiler and the ability to froth milk better (without doing any mods on the Classic). Also you can get better shots from the Silvia, but only if you know how to play/tinker with it. Both of these are great to geek out on! But if you aren't willing to spend time to understand the machine/coffee making, go for the Classic. The Silvia has this thing where when the boiler is empty, it does not autofill unless you do some stuff, which can be damaging to the boiler if you're careless (or too sleepy while handling it).
Silvia vs Oscar - Even though Silvia could only do one thing at a time, some people prefer the Silvia because you're able to play with the temperature more, and get a better shot. Oscar has a better frothing ability, but it's not to say that you can't do a good microfoam on the Silvia. Again the Oscar is less of a hassle for those who just wanna straightaway buat kopi.
I've got a Classic recently, and my priorities were to be able to geek with it. Wasn't keen on forking out an extra 1k for the 'upgrades' in Silvia, nor was I keen on the boiler-refilling-prob (partially cuz i'm careless macam sial wtf). Also, another point of consideration was that the Classic has a lot of replacement parts around and knowledge support, because it's been around for so long. Wasn't a hassle at all to work with it.
For KD-570, it's also known as Sunbeam EM7000 if you wanna look into it further... I think you would be quoted for a bundle too, with a grinder - A friend has that machine and he's happy with it. The bundle came up to 3.5k~, which might be comfortably within your budget. Also can pull a shot and steam milk at the same time. Just make sure that you will get support from the supplier if anything happens. Did consider the BES870, but read reviews that the grinder is not fine enough for espresso.
...which leads to the next point: Grinder > Espresso machine. The Baratza is a great start for grinders! You seem to have done research, so won't repeat what you probably already know. I would go for your second option; cheaper espresso machine and better grinder, esp since you're only using it on weekends.
A two-cents; if you're not willing to go for cheaper espresso machines than your choices here, the Classic is a pretty good deal. It is cheaper than your other options, and gives you room to get a decent grinder + happier wallet. As is, it's good for beginners. Malas oso, boleh guna coffee pods. The selling point for this is that, when your tastebuds become more refined and you yearn for a more cafe-standard espresso, you have the option to make it as such.
Apologies for the wall of text, but I hope this helps. If there are any mistakes, feel free to correct me.
Great! Really appreciated your view, make a lot sen$e to me.
Yes, am aware of WPM is a rebadged of Sunbean, just worry about quality of parts and it's made in china. Taobao is selling. Noticed EM6910 (KD-210S2) has some negative reviews (issues) compare to EM7000. I suppose EM7000 (KD-270) is a newer and better machine?!
May I know how much you paid for Classic? From which seller? I think lazada's price is the cheapest. From the net, there is 2015 version with slight mods/improvements, but feedback was not good (amazon). If I go with Classic, which grinder should I get? Which grinder are you using now?
Cheers.