The majority of clubrooms are higher spec rooms, larger TV screen, extra nespresso type machine alonside kettle/tea/coffee tray, dressing-robes, nicer toiletries, higher+quieter floor, slightly bigger rooms, higher quality/thread-count sheets, whilst they all add up to a better room.
Some hotels it is only the Exec/Club rooms with bath or bath+shower as lower room types are shower cubicle only bathrooms.

As such each upgraded ammenity experience individually is easy to overlook, eg higher threadcount sheets,, but accumulatively room feels that much nicer.

Regards associated club-lounge, none of HI/CP/HIE hotels with lounges need give the associated club room benefits when upgrading you to a club room. If IHG mandated such benefit, hotels with club rooms would simply not upgrade you to them unless to free up lower base rooms to be oversold.
Intercontinental Brand, upgrade to Club Room does not give (except a couple of rare exceptions) the associated Lounge access, even if an Ambassador , let alone lower Spire/Plat non-Ambassador. Only Royal Ambassadors get free Lounge access at IC brand.

Like all hotels, the hotels with lounges may oversell the more basic room types, knowing not every guest can/will pay the extra premium for club room. Giving Club room upgrades as room-only upgrades means hotel can in effect sell 10's of extra base rooms and have higher occupancy and greater income.

If you are a top elite (Plat/Spire) then often the CP that upgrades you to Club Room gives (50% of the time) the lounge access, but not if you have zero status or low status. CP's tend to be nmore generous than HI's i my experience on giving Club+Lounge upgrades