So I browsed in the .xmls a little and found this:
UnitColonyStatDefs.xml
<UnitColonyStats>
<UnitType>Worker</UnitType>
<Stat>
<EffectType>Manufacturing</EffectType>
<Target>
<TargetType>Colony</TargetType>
</Target>
<BonusType>Multiplier</BonusType>
<Value>0.3</Value>
</Stat>
<LevelEffectStats>
<EffectType>Manufacturing</EffectType>
<Target>
<TargetType>Colony</TargetType>
</Target>
<BonusType>Multiplier</BonusType>
<Value>0.01</Value>
</LevelEffectStats>
<NeighborBonuses>
<GiveBonusToNeighborType>Manufacturing</GiveBonusToNeighborType>
<NeighborBonusValue>1</NeighborBonusValue>
</NeighborBonuses>
</UnitColonyStats>
The upper parts detail the stats as one would expect them. The boldly marked ones surprised me. I have not seen any indication of workers (or scientists etc.) increasing any adjacencies.
Is this a bug or intentional, that this is not working?