Further to Hadders' comments, I guess the answer to whether it's worth coughing up for a LIC-LTV season (£144) depends on how many journeys you make on weekdays, on which the £13 minimum fare with a Network Railcard effectively means you get a reduced discount, or none at all!
In essence, any weekday journey you make regularly, where the fare is below £19.70, will get a discount of LESS than 34%. For example, a £15 fare with a Network Card discount reduces to £13, a discount of just 13.33%. With a Gold Card, that fare would reduce to £10. If this journey is one you make reasonably regularly on weekdays, then after 38 such journeys, the additional £3 saving would come to £114 i.e. the difference in price between a Network Railcard and the LTV-LIC Season.
So a huge amount depends on the size of the (undiscounted) fare, and the regularity of the journey undertaken.
If you only ever purchase tickets that have an undiscounted fare greater than £19.70, there's possibly no advantage!