Why not both, as is the case in the Netherlands?
It is quite convenient to be able to show up at a station with a Chipkaart and just rent a bike. Likewise, if you are often making that trip I can imagine that proper and extensive bike storage would be more useful than always renting.
Don't get me wrong, I'm all for hire schemes, I think London's is particularly useful (much less useful in other cities as the centres are more walkable and compact, hence MK's not really working). The problem is that hire schemes pretty much by definition cannot handle pretty much everyone getting off a peak train and wanting a cycle daily. They are based on shared demand which only really works when that demand is spread through the day, and as such only really as a leisure or occasional business travel product.
This was actually designed into the London system - have you ever wondered why the docking stations aren't right outside mainline terminals but rather a short walk away? It's actually to
discourage commuters who are better provided for in their massive numbers by the Tube.
If that doesn't seem obvious, go to London on a Tube strike day and witness the lack of taxis at peak times. While more polluting, they are a limited resource that is shared in the same sort of way and similarly don't handle peaky demand very well.
Cambridge is an odd one. If it was in Europe it'd have an electric tramway, and that'd be the main mode used to get into the centre from the stations. Cycles aren't really good as mass urban transport - they are private transport, just a mode that is more favoured due to its health benefits and lack of pollution.
Actually, I wasn't thinking of the users. The excess manufacture of anything is a global issue: although marginal use of cycles is very environmentally friendly, their manufacture and initial distribution is not, especially if they are made in China. Manufacturing a lot more cycles than is necessary is bad for the planet.
I think you missed my point a little - my point was that for a workable sharing scheme you'd need to manufacture just as many bicycles, and as shared bicycles tend to be more heavily constructed that may not work out quite how you think.
Also note that these "stored" bikes are often old, rusty ones that would otherwise be scrapped, so they may not actually lead to more manufacturing at all. Nobody is going to leave a brand new £5K road bike in the racks at Euston and expect it to be still there tomorrow.
The same applies to the construction of a multi-storey bike park, with the added issue of the opportunity cost: the space taken up by the Cambridge multi-storey bike park could be used in other ways, probably much better uses than as a store for rusting hulks.
That's simply untrue because you could just build on top of it if you wanted more office/residential accommodation.
Actually, not just "could", it's got an Ibis hotel on top of it! (I've stayed there, it's quite nice)
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Google Streetview showing said cycle park with hotel on top