I see both sides. The original design on a family saloon is always likely to be a compromise and as "old Engineer" stated has to consider the effect on the direct suspension components and transfer of vibration, shock and noise to other components and occupants as well as a huge variety of road surfaces.
Whilst UK roads aren't perfect they are far better than the roads of many other countries.
I think it it a personal preference, read the threads, make up your mind and do what you think is right for you. When mine go I will probably polybush.
I do not think Alfa Engineers are always right for every situation. For long term Alfa owners I am sure we can all come up with some Afla designs that are just plain rubbish and others that are stunning but, if you do play that game be careful of coming up with components that aren't Alfa.
I also agree with both sides of the comments about Colin Chapman using rubber donuts. Yes they will protect other components but does anyone here know enough to be certain why he chose donuts. Perhaps on these high performance (for the day) cars in the drive for light weight versus reliability the other components may have been designed right on the edge of reliability and donuts were an essential component to protect clutch, gears and differentials or perhaps they were the lightest solution thus aiding performance. The Lotus example probably shows you can't take a single component example, you MUST know what design tolerance is built into the other components.
Some will think this will support NOT polybushing (we can't be certain what safety tolerance is in the other components) but I suspect that on a car like the 159 sold worldwide to cope with huge variations in road conditions there will be quite significant durability built into the surrounding components. Oh I might have forgot the M32 gearbox but I haven't forgot that this component isn't an Alfa design.
Alfa Romeo announced the next four models to be released will be fitted with revolutionary Polyurethane Bushes. The Company has decided not to restrict there usage to suspension components, but instead will be fitting them to all engine mounts and braces and couplings for propeller shafts for these rear - wheel drive models. Asked why, there had been such a dramatic seed change in their engineering approach, a spokesman was quoted as saying, "Well if we are going to shake the hell out of our cars and their passengers, we might as well do a proper job. The Engineering boys have been getting bored of late, and our New C.E.O. thinks it would be a good idea to re-visit these issues, which hitherto we felt had been resolved. Who knows, we may ultimately discover, the best shape for a wheel is Hexagonal. This is all part of Alfa Romeo's drive to be seen as an Environmentally Friendly Company. All rubber components will be removed from our vehicles and as the intention is to "firm - up the ride", tyres will no longer be Pneumatic. They too can be made of Polyurethane."
Mechanical vibrations are by their very nature, low frequency. Such frequencies, when coupled to components, which have low Resonant Frequencies, can result in the magnification of these frequencies as a function of the so called "Q - Factor". Such is the nature of a resonating body; Electrical or mechanical, the magnitude of power in a body; at resonance, is multiplied many, many times, potentially resulting in the body self destructing. So the function of a rubber bush is manifold; it must transfer the torque, absorb shocks and absorb harmonics which ultimately could cause any part of a dynamic body to approach resonance.
A solid bush has a "Naturally High Resonant frequency", well beyond the frequencies induced as a function of reciprocating masses such as exist in cars. So they have virtually no positive effect in eliminating these mechanical harmonics (frequencies). The wrong rubber bush can be equally disastrous; I could quote several instances where I have first hand experience of this. However, when the appropriately designed "Rubber composite" bush is fitted to reciprocating components, it diminishes these harmonics which could lead to the mechanical body(s) resonating. Shock absorbers are the most obvious example we all aware of. But it is no different elsewhere in a car's construction. Colin Chapman knew that.