There's a lot to be said about this. But one thing that I disagree with is that there "may or may not be a reduction in the effectiveness of combo."
To my knowledge there has never been a time in the history of Magic where the DCI has
Restricted cards and sped up the format as a result. Due to the power/noninteractive nature of almost every archetype at this point it would make sense that the DCI would take steps to reduce the consistency/speed/power of each Archetype to the point where it would be forced to at least pretend to interact with its opposition. There will be hue and cry for a period of time but at least order will be restored and the malaise that is currently affecting the entire community may be lifted and cards that were previously ignored due to their relative lack of power in comparison to older cousins will come to the fore. See the Vintage forum thread started by Smmenen to get a flavor of the vintage intelligentsia's general disaffection with the situation, and the need for drastic change becomes evident.
For me the current dilemma can be summed up by looking at Trinishere. This card is actually a marvel of design. It has a powerful effect but the effect is greatly reduced in power as the game goes on.
Whoa there tiger. "Marvel of Design?" I think not. The decks designed to abuse the power of the sphere almost never relinquish control of the game to such a degree that the Sphere's effect becomes irrelevant if it's in play. IMHO the Sph3re may have been created in a vacuum without the thought that it might have an immense impact on vintage. I could see it having been the earliest attempt on the part of Wizards to limit the power of Affinity in standard, sort of a less-sucky Hum of the Radix. Given the existence of Sphere of Resistance was it really necessary to print this monster? That answer probably lies above my paygrade.
First of all, I don't want to hijack JP's thread, my points of view are there to be shot at in the thread in Community, which is a far more open one than this. JP's article was excellent and I just wanted to agree with him. He certainly didn't sign up to Trinisphere design praise.
To answer the above points, whilst still trying to be relevant to this thread.
1. Combo could get hit by restrictions and become stronger. Look at Highlander (Vintage with the Biggest B&R list possible). Tendrils Combo was too strong. Everything restricted and yet too strong. When talking about a wave of restrictions, it is important to understand that decks that are full of ways of finding cards like combo don't get hit as hard by restrictions as decks like control do (look at the numbers of Tendrils vs the numbers of Mana Drains/Workshops). Are you really achieving anything by 'slowing down the fundamental turn' which may or may not be practical, when the result is that you allow combo the luxury of more time to go off, safe in the knowledge that an early Trinisphere or an early Mana Drain or an early Welder are far less likely? I don't know, but I do know that in the format that was Vintage with everything restricted, combo WAS the monster that was out of control.
2. I stand by my statement that Trinisphere is a marvel of design and am glad that you pointed out how good it is in decks designed to use it. That is the sign of a good card. I would look at Black Vise and Skullclamp and the fact that they were insperted into just about anything as a sign of badly designed (more specifically developed as Vise for 2 mana and Clamp with an extra mana on activation or just +1/0 would have been far more acceptable). You just can't design decent cards that are usable in Vintage if you start with the assumption that you can generate 3 mana on turn 1. 3sphere at 4 mana is a pile of poo.
I think the main point of this thread is that there are no easy answers and the solution rather depends on where you want the format to go, a goal that is by no means uniformly agreed. It is certainly true that the format is now where most people asked for it to be, and many of those who pleaded for the change aren't very happy with what they got.
I would just like to add that I think that cards can be restricted even if that restriction has a minimal effect on the format, simply because that card deserves restriction. I honestly believe that Workshop deserves restriction on power level alone but might deserve the 'Mana Drain' treatment of being left alone in order to preserve the balance of the format. I do not believe that restricting Workshop would result in little to no change due to Ancient Tomb as many have stated.
Apologies for the length of my post!