I'm the same as you Jerry. Whilst it is very much needed, other options need to be explored. But I do think any money needs to specifically be put into alleviating the congestions through Newport rather than on other projects. Traffic as it is, is already bad enough. With the recent influx of people moving the Welsh side of the bridge, and that likely continuing to happen for some time, it's only going to get worse.
With that in mind, better transport links may need to be looked at, especially for those commuters heading from South East Wales to Bristol. Anyone in the Chepstow area would need to change trains at Severn Tunnel Junction for Temple Meads or further South, or Newport for Bristol Parkway and further East. The current train network leaves a lot to be desired, but recently GWR have increase capacity on their trains to Temple Meads, and the various improvements with new trains on the London Mainline. There's currently no link for Newport Valleys from Ebbw Vale in to Newport, which is in the pipeline over the next few years.
Options for freight should be looked at to reduce lorry usage.
A bus link with a slight local element needs to be looked into, starting at Newport or even Cardiff, with some en route stops such as Newport East, Magor & Chepstow and local stops en route heading from Avonmouth and in to Bristol City Centre. The direct bus route was lost when First lost the Airport contract and the current National Express to BRS now bypasses the City Centre.
Secondly it's an alternative for anyone driving through the tunnels heading North that would come off at the Coldra onto the A449/M50. It has been suggested improving this access by bypassing over the North of Newport or even as far up as the Valleys.
There is however the issue of Cardiff's profile in hosting events. Traffic from the East can be a nightmare in the run up to special events in the city. That's where the tunnels really cause a problem.
The Newport Distributor road was a good investment previously, but i don't think it's now serving it's purpose. As it's still an A road, there's a number of pinch points along the route through various roundabouts and junction, which causes tailbacks on that route as well. An improved, dual carriage route, with fewer pinch points shouldn't mean too much amendments and will help the traffic flow as an alternative route around the tunnels.