As I have said previously on this site, political parties for specific groups within society do not work in the sense of gaining power and influence. Yes, there is publicity to be gained for the cause by fielding candidates at an election, but once the election has gone, and you have gained a few hundred votes (or thousands if you are very lucky), all will be forgotten and you will be no nearer achieving your aims.
You say that the Pensioner's Party is not a single issue party. No, it is not, but the only one's who will vote for the Pensioner's Party are those who believe that the treatment of Pensioner's is the most pressing issue of the day.
The policies as stated on their website are not much more that a list of ideas, and do not address many of the major issues of the day - the economy, cost of housing, the environment, creeping privatization of schools and hospitals, etc, etc. Whilst putting forward policies to improve the lot of pensioners, it is totally silent on the plight of other low income groups who are having an equally hard time as many pensioners are.
The other critical point is that pensioners are not a homogenous group. There is as wide a difference in circumstances between individuals as in any other age group.
Whilst the choice of parties to vote for is totally uninspiring, I for one would certainly not vote for this party. If others on this forum want to put up coherent arguments against my position, I would be happy to debate.