Hiya,
As a recent first time joiner of the WP club, I can fully understand your situation.
I went through this exact train of thought about 3 years ago, when there was a bigger gap between SG and WP benefits.
I ended up earning around 1100 SC's and was sorely tempted to go the extra, but of course, did not do it in the end. For me, it was fortunate, as the global financial crisis came and wiped out corporate travel, and I would have wasted the points/money. I was comp'ed an extra year in SG, then soft landed into PS.
I am still yet to visit the Flounge, and anticipate doing so this Sunday. However, my flight is at 10am on CX, probably have to leave the lounge at 9:30am. If I leave home at 8am, allowing 30mins to get to the airport, and another 30mins to get through to airside, then I only get a measly 30mins in the lounge. I would have eaten brekkie at home, and there's not really enough time to go the spa (and wouldnt know what they do there anyway).
Net benefit in Sydney = none.
I have a couple of hours waiting in HK for a connecting flight. This should be where I see CX's differential between J and F lounge for the first time. I hope to get a decent meal out of it, but I know the Jlounges are perfectly fine.
Not sure of your circumstances, but you might be better off saving the points/money to ensure you requalify for SG next year? I rate the benefits of SG much better than PS.
Hope that 2 cents helps.