I've started doing this. I ran the numbers and it's still worth doing from my perspective, as you are getting investment growth on the tax relief element.
Caveats:
1. IHT - the planned changes probably mean that it's not worth doing for most investors. Mine's all going to charity, so not an issue. Bear in mind though, that the changes may not happen - they are proposals only at this point. So you risk missing out on a couple of years' worth of contributions.
2. Time horizon. If you plan to withdraw in less than about 10 years then it may not be worth it.
As regards the pension recycling rules, it's not an issue as the amount is below the threshold (which I think is £7.5K if I recall correctly). (Also, if your tax free cash from the rest of your SIPP was taken more than 2 years ago, it's not an issue anyway.) As always though, watch out in case the rules change.
Edit:
Just to add a third consideration: if you have already taken around / over £100K in tax free cash, bear in mind that if they do decide to restrict tax free lump sums, it won't be worth adding to SIPPs.