Good marketing should always encompass regular offers / discount periods... like stores, its when you often do your biggest sales periods, especially if you pre-advertise it first. A nice PRWeb release a month before sale would do the job for online purposes, just like stores do in local papers and TV weeks prior to huge sale promotions.
Bit late to the thread but I must respectfully disagree. Software like XenForo is quite different to most other retail items.
Random example - if you buy a pair of shoes in the sales, things to consider:
a) The shoes will have a fixed life span (or repair costs if they are a good pair of work shoes etc...)
b) It's "this seasons" design. A new design/revision will appear next season, for people to purchase.
c) There's generally no need for aftersale. You won't normally need to call or email customer services and ask how to tie the laces etc...
If a shoe shop is getting ready to take stock of the next seasons goods, they don't want old stock hanging around people will no longer want and also need to make room on their physical shelves (whether it's retail or online e.g. amazon - still needs space!).
As XenForo includes a subscription with access to future releases for a year, it doesn't go out of date. There also isn't a finite number of XenForo licenses like you have with 'retail' products. By running sales you run the risk of devaluing your product - people would stop thinking of the $140 price as the cost of XenForo, and instead at $100-120 or whatever the regular sale price happened to be. Yes, you might get more sales when you run a promotion, but the flip side is you could reduce the number of purchases when you aren't running a promotion - as people decide to hold off for the next one. That's not really good from a cash flow point of view (the reason most businesses fail).
I've worked for a number of businesses that sell invoicing and billing software products - one company ran promotions pretty often. It devalued their product (and also hurt second hand license values) and lead to pain for everyone. As a result, the company has more or less stopped trading. Another company ran a couple of sales every year which was fine - except people would then demand the same discounts the rest of the time or ask "you ran a sale at this time last year... why not another? I wanted to get a license now!" etc....). Or "why only a 15% discount now, last time it was 20% etc..". Just a big headache! And when it's a case of do you provide no discount, and risk losing that sale, or get 90% of the sale price and give in - that's not an easy decision when times are a bit difficult and/or there are targets to hit! For the company I work at now, I finally got it agreed that we'd more or less stop discounting in nearly all circumstances. It probably goes against what all the "marketing guru's" out there say, but in our case it's been a huge success. Sure, we've lost some sales - but we're actually taking in more cash and supporting fewer customers (so our costs are lower). Sure, we might not be growing as fast customer number wise - but it seems more sustainable.
Now... you can mitigate things like this with coupons etc... Or simply increasing your selling price so that the discounted price is still acceptable. But for a small company starting out without huge financial backing, unless you have the time (and I'd say someone dedicated to working on it) to organise your marketing and pricing, it's much simpler to focus on producing a good product, getting sales at a set price, and leaving the rest to word of mouth. It's worked well in my own personal experience, it seemed to work well for vBulletin in the past, and I'd bet it would work for XenForo too. Sometimes... I think simpler might just be better
(as a small side note - I also actually worked for a large retailer many years ago. We were well known for providing discounts, people just had to push us a bit. A few clicks on the till and they'd suddenly walk out with 5-10% off. The company changed policy - reducing prices slightly, scrapping discounts, and stopping the constant "promotions" which had previously been well advertised on TV / newspapers etc... Sales were up across the chain, average transaction values up, and profit went up quite a bit too.).