Trying to put a value on Avios depends upon what you intend to use the points for.

For example, if you book a last minute flight: e.g.:

BRU to NCL on Tuesday in ET is €436. In CE, it is €644.

Alternatively, you can redeem 2250 Avios plus €42.50 euros for ET, or 4500 Avios plus €72.50 for CE.

That puts a value on the Avios as €175 per 1,000 (ET) and €127 per 1,000 (CE).

Which means that your 3,000 Avios potentially have a value of €525!

However, those same flights can be bought for significantly less if booked just a bit ahead of time.

In general, there seems to be a consensus in this forum that using Avios for upgrading flights gains the most value. Also, booking last-minute intra European flights - especially to UK regions - puts the Avios points to good use.

To answer your question specifically: irrelevant of the above, I value Avios at £20 per 1,000. That means your 3,000 Avios (to me) are worth £60. With the exception of a possible op-up (unlikely) there are no other benefits that I can see from getting to silver before your trip. As a 'mileage run' will more more than likely cost you more than £60 (if you value the extra 3,000 Avios you will gain at circa £60) it seems a bit of a waste of time to me.