You need to have a look around sometime , it is an interesting line and of course St Albans has many attractions.
Buses are fine off peak in this area , but the last mile into Watford and SAC are an absolute killer , - Watford has been encircled by a terrible ring-road which acts as a Berlin Wall for pedestrians and the approaches from Garston are log-jammed , SAC has the previously mentioned medieval street pattern and IMHO the worst driving standards in the UK. An awful combination.(especilally this am at 0745 when I did 2 related work journeys for family members in this dire weather)
The bus "station" at Watford Junction does exist , but is a disgrace with minimal facilities and a standard of cleanliness that defies description , SAC though does have a decent enough interchange in front of the station.
So while the solum of an Abbey line busway - is maybe do-able , (thinking of bridges and especially the one over the M25 !) , the lack of access to the commercial and working areas remains a complete disincentive. Walking is usually the best option for "Local" journeys , - though my detailed knowledge of the line (having managed it operationally for some years) , indicates that the Watford end - unsurprisingly - has the higher transfer rate to the rail system.
The Watford station area has considerable development (non retail) going on - apart from hotels and £300,000 affordable flats , more office space. Road congestion is not going to get better.